## 3 Results and Discussion
### Content of Glucans  
In order to further characterize the carbohydrates contained in _A. platensis_ after phosphorus limitation, two different assay kits were used (see Material and Methods section). The assays revealed that there was an absolute absence of 1.3:1.4-\(\beta\)-D-glucans (not detectable by the assay kit used), while the content of \(\alpha\)-, and 1.3:1.6-\(\beta\)-glucans varied significantly (Table 2). The total glucan content displayed an inverse relationship with the phosphorus concentration, i.e., at higher degrees of phosphorus limitation the content of glucans was higher. The same trend was observed for each individual type of glucans measured, namely, \(\alpha\)-glucans and 1.3:1.6-\(\beta\)-glucans, with the only exception being that at 4 mg-P/L the content of \(\alpha\)-glucans was the same as the control. Since the content of \(\beta\)-(1.3:1.6) and \(\alpha\)-glucans showed the same trend, their ratio was calculated and illustrated in Figure 2 as a function with phosphorus availability. As shown, the \(\beta\)/\(\alpha\)-glucans ratio was positively related to phosphorus availability, which means that the proportion of \(\alpha\)-glucans was higher in the cultures with a higher degree of phosphorus limitation. However, the ratio \(\beta\)/\(\alpha\)-glucans in the control culture did not follow this trend, indicating that there was an unbalanced accumulation of \(\alpha\)- and \(\beta\)-glucans. Given that the \(\alpha\)-glucans content of the cultures with 4 mg-P/L was almost the same as the control cultures, this might suggest that under moderate degrees of P limitation, first \(\beta\)-glucans start to accumulate and then as the degree of P limitation increases the \(\alpha\)-glucans also start to increase in an unbalanced pattern of \(\alpha\)- and \(\beta\)- glucans. Figure 3 illustrates the proportion of total glucans compared to the total carbohydrates of _A. platensis_. As shown, at higher degrees of phosphorus limitation, the proportion of glucans was lower (around 65-68%) in comparison to the less stressed cultures where the proportion was higher (around 75%) or compared to the control (80%). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**P-Concentration** & **Total Flucans (\%\({}_{\text{DW}}\))** & **Total Carbohydrates** & **Total Lipids (\%\({}_{\text{DW}}\))** \\ \hline
1.5 & 22.45 \(\pm\) 3.55 & 65.25 \(\pm\) 3.88 & 5.56 \(\pm\) 1.03 \\
2 & 23.09 \(\pm\) 1.57 & 65.01 \(\pm\) 3.24 & 6.68 \(\pm\) 1.16 \\
3 & 25.88 \(\pm\) 1.99 & 51.06 \(\pm\) 3.24 & 7.98 \(\pm\) 1.66 \\
4 & 33.02 \(\pm\) 2.91 & 33.42 \(\pm\) 2.67 & 7.38 \(\pm\) 1.98 \\
89 (Control) & 59.03 \(\pm\) 3.61 & 23.04 \(\pm\) 1.95 & 8.58 \(\pm\) 1.43 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Biochemical composition of _A. platensis_ cultivated in semi-continuous mode with different phosphorus concentrations. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**P-Concentration** & **Total Flucans (\(\alpha\) + \(\beta\))** & **1.3:1.6-\(\beta\)-Glucans** & **1.3:1.4-\(\beta\)-Glucans** & **\(\alpha\)-Glucans** \\ **(mg-P/L)** & **(\%\({}_{\text{DW}}\))** & **(\%\({}_{\text{DW}}\))** & **(\%\({}_{\text{DW}}\))** & **(\%\({}_{\text{DW}}\))** \\ \hline
1.5 & 42.96 & 30.98 \(\pm\) 1.56 & Not detectable & 11.98 \(\pm\) 1.55 \\
2 & 44.56 & 33.62 \(\pm\) 0.63 & Not detectable & 10.94 \(\pm\) 0.84 \\
3 & 35.17 & 27.88 \(\pm\) 0.16 & Not detectable & 7.29 \(\pm\) 0.18 \\
4 & 24.97 & 20.30 \(\pm\) 1.43 & Not detectable & 4.66 \(\pm\) 0.07 \\
89 (Control) & 18.54 & 13.72 \(\pm\) 0.40 & Not detectable & 4.82 \(\pm\) 0.57 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Content of glucans in _A. platensis_ cultivated in semi-continuous mode with different phosphorus concentrations. So far, the storage polysaccharides of _A. platensis_ are considered to be glycogen, which is comprised mainly of glucose units linked through 1,4-\(\alpha\) glycosidic linkages and branched through 1,6-\(\alpha\) glycosidic bonds [28; 34; 35; 36]. However, more recently the study of [PERSON] et al.