COMPARISON OF TETRAPLOID AND SINGLE GENE‐INDUCED GIGAS VARIANTS IN CHICKPEA (CICER ARIETINUM). II. MORPHOLOGICAL AND ANATOMICAL LEAF CHARACTERS

Two genomic variants of a chickpea (Cicer arietinum L.) parental line have been developed which exhibit gigas characters. The two genotypes were the result of a single-gene mutation (gigas) and induced tetraploidy of a single parental line. The two genotypes plus parental strain were investigated to determine the similarity-of-effect ofpolyploidy and this single-gene mutation on leaf anatomy and morphology. Leaves consisted of two rows of alternatively arranged leaflets. Both the tetraploid and parental lines had the same mean number of leaflets per leaf while the gigas plants had fewer, but mean total leaf surface area was greater in the gigas plants. Quantitative comparison of mesophyll and vascular tissue and air space volume density (Vv) showed that leaves of the tetraploid plants had the greatest mesophyll cell density (Vvm) and least air space density. Mesophyll cell density was equal in the parental and single-gene mutant while parental leaves had the greatest vascular tissue density. The greater mesophyll cell density values of the polyploid were due to larger mean mesophyll cell size, not to greater cell numbers per unit area. Leaf models based on tissue density and leaflet size showed tetraploid plants had the greatest productivity potential per unit of leaflet surface area. However, if models were based on a whole leaf, gigas plants had the greatest productivity potential since they had larger total leaf area. The effectiveness of using structural models to predict physiological potential in plant tissues will be tested in future studies. A CHICKPEA (Cicer arietinum L.) variant with enlarged leaves, pods, seeds, and flowers was derived from wild type parental line (ICC 640) following gamma-irradiation of seeds (Davis, Matthews, and Fagerberg, 1990). This truebreeding gigas variant, designated PM 1 101, resembles closely the gigas mutants described by Argikar (1952) and Athwal (1963). Because the gigas characteristics of PM 1101 are the pleiotropic effects of a single-gene mutation (Davis et al., 1990), a detailed comparison of leaf structure in PM 1 101 and its parent line ICC640 might reveal clues to the mechanism of differential gene action in these near isogenic lines. Extension of this comparative study to include an autotetraploid derivative of diploid (2n = 2x = 16) ICC640 might reveal important differences in the way two contrasting types of genetic change, single-gene mutation and tet' Received for publication 31 October 1988; revision accepted 7 September 1989. The authors would like to thank Brenda Giust and Dawn Allain for their technical assistance on this project. Contribution number 1588 from the Agricultural Experiment Station, University of New Hampshire, Durham, NH 03824. 2 Current address: Dept. of Agronomy, University of Missouri, Columbia, MO 65211. raploidy, can translate into enlargement of an important plant organ, the leaf. In chickpea, effects of colchicine-induced tetraploidy include dark green foliage, and enlarged seeds, leaflets, stomatal guard cells, and pollen grains (Sohoo, Athwal, and Chandra, 1970; Pundir, Rao, and van der Maesen, 1983; Bahl, 1987). Molin et al. (1982) found that tetraploid alfalfa populations had approximately twice the DNA, ribulose bisphosphate carboxylase (RuBisco), chlorophyll and chloroplasts per cell as the diploid plants. Photosynthesis-derived ?2 evolution in the tetraploid alfalfa plants also was approximately twice that in the diploid plants. Changes in leaf compartment size may affect leaf physiology (Boardman, 1977) in a number of ways: gas diffusion within the leaf as determined by mesophyll surface area, air space within the leaf, and stomatal resistance; light refraction within the leaf (mesophyll cells acting like miniature lenses) which may change the photon-flux density within the leaf (Vogelman and Bjorn, 1984, 1986); a larger mesophyll compartment which would provide space for greater numbers of organelles (e.g., chloroplasts-Fagerberg, Moon, and Truby, 1979; Fagerberg, 1987, 1988b). Although it is not yet clear how leaf anatomy is regulated, it