title: Carbohydrate storage and remobilisation: The mechanisms involved in woody stem tissue of apple trees

authors: McQueen, Joanna C.

abstract: This thesis investigated the storage and remobilisation of carbohydrate reserves in perennial woody stem tissue, using one-year-old apple stems. In this study, the theories developed in herbaceous annual species were applied to woody perennial plants. Perennial plants are more complicated to study as they need reserves over a longer temporal scale and the woody tissue makes experimental manipulation difficult. In addition, apple is a multiple carbohydrate transporter and sorbitol (a sugar alcohol) is a major translocation product. These complications were overcome in this thesis, allowing hypotheses, developed from knowledge of carbohydrate movement in herbaceous plants, to be tested. The hypotheses were tested by manipulating sink conditions, 14C and 11C tracer experiments, use of inhibitors and enzyme extractions. 
The findings allowed models of carbohydrate storage and remobilisation in stem tissue of apple to be made. The sieve elements of apple are leaky pipes and assimilates are lost through passive leakage or active unloading during their journey from source to terminal sink. During remobilisation of carbohydrate in spring, retrieval of this leaked assimilate back into the phloem stream is up-regulated. This retrieval is likely to be directly into the sieve elements and involves carriers similar to those found in herbaceous annuals. Buffering also occurs along the stem length to prevent interruption to flow from short-term changes in photoassimilate supply. Buffering, leakage and retrieval probably occur into the apoplast. Starch is initially remobilised from storage cells closest to the phloem region in the spring. Sorbitol in the stem probably cannot be metabolised, which allows sorbitol to exist in high concentrations in the stem where it could act as a temporary (days to weeks) storage pool and could play a buffering role, maintaining a constant flow of sorbitol to sink tissue. 
During storage in autumn, when terminal sink tissue is either removed or saturated, assimilates continue to be lost from the leaky sieve tubes. However, retrieval is down-regulated so high concentrations of sugars build up in the stem apoplast. This results in storage of carbohydrate as starch, initially into the cells surrounding the phloem. Storage in the stem is given the lowest priority in terms of accumulating available carbohydrate and only occurs when there is an excess of photoassimilate, such as when higher priority sinks like fruit are removed or saturated. Eventually starch storage will saturate (at a concentration of 50mg g-1 in trees growing in the Hawkes Bay). Saturation of storage is likely to reduce concentration gradients between sieve elements and the apoplast, leading to a build up of sugars in the sieve elements and reduced assimilate flow. This is likely to result in a reduction or stoppage of photosynthesis, followed by leaf senescence. 
The results of this thesis show that most of the processes of carbohydrate storage and remobilisation in herbaceous plants also occur in woody perennial plants and this has increased our knowledge of basic plant processes. In order to manipulate source-sink relationships in plants to increase crop yields, we need to understand the physiological processes involving the movement of carbohydrates. The retrieval and release of sugars along the transport phloem is important, as there is a balance between supplying terminal sinks with photosynthate and retention of photosynthate along the pathway. In addition, physiological studies into apple trees are sparse. It was important to go to the next stage of carbohydrate studies in apple trees, beyond orchard management, and understand the physiological processes involved in carbohydrate movement and remobilisation. Apple is a high yielding crop and knowledge of the carbohydrate processes in this plant could help to increase yields in other commercially important tree species.

text: Carbohydrate storage and remobilisation: The mechanisms involved in woody stem tissue of apple trees This thesis investigated the storage and remobilisation of carbohydrate reserves in perennial woody stem tissue, using one-year-old apple stems. In this study, the theories developed in herbaceous annual species were applied to woody perennial plants. Perennial plants are more complicated to study as they need reserves over a longer temporal scale and the woody tissue makes experimental manipulation difficult. In addition, apple is a multiple carbohydrate transporter and sorbitol (a sugar alcohol) is a major translocation product. These complications were overcome in this thesis, allowing hypotheses, developed from knowledge of carbohydrate movement in herbaceous plants, to be tested. The hypotheses were tested by manipulating sink conditions, 14C and 11C tracer experiments, use of inhibitors and enzyme extractions. 
The findings allowed models of carbohydrate storage and remobilisation in stem tissue of apple to be made. The sieve elements of apple are leaky pipes and assimilates are lost through passive leakage or active unloading during their journey from source to terminal sink. During remobilisation of carbohydrate in spring, retrieval of this leaked assimilate back into the phloem stream is up-regulated. This retrieval is likely to be directly into the sieve elements and involves carriers similar to those found in herbaceous annuals. Buffering also occurs along the stem length to prevent interruption to flow from short-term changes in photoassimilate supply. Buffering, leakage and retrieval probably occur into the apoplast. Starch is initially remobilised from storage cells closest to the phloem region in the spring. Sorbitol in the stem probably cannot be metabolised, which allows sorbitol to exist in high concentrations in the stem where it could act as a temporary (days to weeks) storage pool and could play a buffering role, maintaining a constant flow of sorbitol to sink tissue. 
During storage in autumn, when terminal sink tissue is either removed or saturated, assimilates continue to be lost from the leaky sieve tubes. However, retrieval is down-regulated so high concentrations of sugars build up in the stem apoplast. This results in storage of carbohydrate as starch, initially into the cells surrounding the phloem. Storage in the stem is given the lowest priority in terms of accumulating available carbohydrate and only occurs when there is an excess of photoassimilate, such as when higher priority sinks like fruit are removed or saturated. Eventually starch storage will saturate (at a concentration of 50mg g-1 in trees growing in the Hawkes Bay). Saturation of storage is likely to reduce concentration gradients between sieve elements and the apoplast, leading to a build up of sugars in the sieve elements and reduced assimilate flow. This is likely to result in a reduction or stoppage of photosynthesis, followed by leaf senescence. 
The results of this thesis show that most of the processes of carbohydrate storage and remobilisation in herbaceous plants also occur in woody perennial plants and this has increased our knowledge of basic plant processes. In order to manipulate source-sink relationships in plants to increase crop yields, we need to understand the physiological processes involving the movement of carbohydrates. The retrieval and release of sugars along the transport phloem is important, as there is a balance between supplying terminal sinks with photosynthate and retention of photosynthate along the pathway. In addition, physiological studies into apple trees are sparse. It was important to go to the next stage of carbohydrate studies in apple trees, beyond orchard management, and understand the physiological processes involved in carbohydrate movement and remobilisation. Apple is a high yielding crop and knowledge of the carbohydrate processes in this plant could help to increase yields in other commercially important tree species.

year: 2003

title: Genomic signals of local adaptation across climatically heterogenous habitats in an invasive tropical fruit fly (Bactrocera tryoni)

authors: Parvizi, Elahe

abstract: Local adaptation plays a key role in the successful establishment of pest populations in new environments by enabling them to tolerate novel biotic and abiotic conditions experienced outside their native range. However, the genomic underpinnings of such adaptive responses remain unclear, especially for agriculturally important pests. We investigated population genomic signatures in the tropical/subtropical Queensland fruit fly, Bactrocera tryoni, which has an expanded range encompassing temperate and arid zones in Australia, and tropical zones in the Pacific Islands. Using reduced representation sequencing data from 28 populations, we detected allele frequency shifts associated with the native/invasive status of populations and identified environmental factors that have likely driven population differentiation. We also determined that precipitation, temperature, and geographic variables explain allelic shifts across the distribution range of B. tryoni. We found spatial heterogeneity in signatures of local adaptation across various climatic conditions in invaded areas. Specifically, disjunct invasive populations in the tropical Pacific Islands and arid zones of Australia were characterised by multiple significantly differentiated single nucleotide polymorphisms (SNPs), some of which were associated with genes with well-understood function in environmental stress (e.g., heat and desiccation) response. However, invasive populations in southeast Australian temperate zones showed higher gene flow with the native range and lacked a strong local adaptive signal. These results suggest that population connectivity with the native range has differentially affected local adaptive patterns in different invasive populations. Overall, our findings provide insights into the evolutionary underpinnings of invasion success of an important horticultural pest in climatically distinct environments.

text: Genomic signals of local adaptation across climatically heterogenous habitats in an invasive tropical fruit fly (Bactrocera tryoni) Local adaptation plays a key role in the successful establishment of pest populations in new environments by enabling them to tolerate novel biotic and abiotic conditions experienced outside their native range. However, the genomic underpinnings of such adaptive responses remain unclear, especially for agriculturally important pests. We investigated population genomic signatures in the tropical/subtropical Queensland fruit fly, Bactrocera tryoni, which has an expanded range encompassing temperate and arid zones in Australia, and tropical zones in the Pacific Islands. Using reduced representation sequencing data from 28 populations, we detected allele frequency shifts associated with the native/invasive status of populations and identified environmental factors that have likely driven population differentiation. We also determined that precipitation, temperature, and geographic variables explain allelic shifts across the distribution range of B. tryoni. We found spatial heterogeneity in signatures of local adaptation across various climatic conditions in invaded areas. Specifically, disjunct invasive populations in the tropical Pacific Islands and arid zones of Australia were characterised by multiple significantly differentiated single nucleotide polymorphisms (SNPs), some of which were associated with genes with well-understood function in environmental stress (e.g., heat and desiccation) response. However, invasive populations in southeast Australian temperate zones showed higher gene flow with the native range and lacked a strong local adaptive signal. These results suggest that population connectivity with the native range has differentially affected local adaptive patterns in different invasive populations. Overall, our findings provide insights into the evolutionary underpinnings of invasion success of an important horticultural pest in climatically distinct environments.

year: 2024

title: Leadership: Going beyond personal will and professional skills to give life to Ka Hikitia

authors: Berryman, Mere

subjects: education policy

abstract: This paper investigates the Ka Hikitia Māori education policy and its subsequent influence in effecting system change towards Māori students’ achievement. It discusses how a Request for Proposal to the Ministry of Education’s Building on Success was conceptualised to support English-medium secondary schools across New Zealand to address this policy. The result, Kia Eke Panuku, is a professional learning and development response that works with Strategic Change Leadership Teams to create culturally responsive and relational contexts for learning, focused on Māori students enjoying and achieving educational success as Māori. It is argued that neither a political mandate for change nor a set of learned strategies by school personnel will truly bring about a changed reality for Māori students. Rather the reform must be led by transformative leaders who are driven by both the moral imperative to change and a keen sense of urgency to see this happen in our schools for Māori students and their home communities.
The major issues raised in this paper, and the solutions that have been reached thus far, can help inform others who are trying to raise the participation, inclusion and achievement of students who may currently be marginalised from formal education settings.

text: Leadership: Going beyond personal will and professional skills to give life to Ka Hikitia This paper investigates the Ka Hikitia Māori education policy and its subsequent influence in effecting system change towards Māori students’ achievement. It discusses how a Request for Proposal to the Ministry of Education’s Building on Success was conceptualised to support English-medium secondary schools across New Zealand to address this policy. The result, Kia Eke Panuku, is a professional learning and development response that works with Strategic Change Leadership Teams to create culturally responsive and relational contexts for learning, focused on Māori students enjoying and achieving educational success as Māori. It is argued that neither a political mandate for change nor a set of learned strategies by school personnel will truly bring about a changed reality for Māori students. Rather the reform must be led by transformative leaders who are driven by both the moral imperative to change and a keen sense of urgency to see this happen in our schools for Māori students and their home communities.
The major issues raised in this paper, and the solutions that have been reached thus far, can help inform others who are trying to raise the participation, inclusion and achievement of students who may currently be marginalised from formal education settings.

year: 2015