3.3. Photosynthetic energy partitioning
The contribution of the different pathways to energy partitioning in PSII complexes is shown in Fig. 3. Iron deficiency reduced the photochemical efficiency of PSII in light-adapted leaves (II) in both leaf regions checked, with a more drastic effect in the interveinal areas than in the midrib. At day 42, the decrease in II was about 64% in the midrib of Fe(−) leaves, while in the interveinal area the decrease reached 92%. This pronounced decrease in II resulted from changes in the total non-photochemical quenching capacity (NPQ + NO). In midribs the pattern of quantum yield of regulated energy dissipation (NPQ) was quite similar in all screened leaf areas, and NPQ values remained relatively stable till recovery (day 50), when a significant increase occurred. In contrast, in interveinal areas, NPQ values displayed variability throughout the study and showed some heterogeneity. In fact, NPQ values decreased significantly in a first phase (day 20), and then began to increase until it reached values that were not significantly different from the Fe-sufficient treatment at days 42 and 50. Quantum yield of non-regulated energy dissipation (NO) was enhanced considerably by Fe deprivation, with the highest values in extremely deficient plants. One week after Fe resupply, NO returned to values analogous to those of Fe(+) plants, but II, despite a significant increase in their values, did not recover completely because values of NPQ remained high.
3.3. Photosynthetic energy partitioning
The contribution of the different pathways to energy partitioning in PSII complexes is shown in Fig. 3. Iron deficiency reduced the photochemical efficiency of PSII in light-adapted leaves (II) in both leaf regions checked, with a more drastic effect in the interveinal areas than in the midrib. At day 42, the decrease in II was about 64% in the midrib of Fe(−) leaves, while in the interveinal area the decrease reached 92%. This pronounced decrease in II resulted from changes in the total non-photochemical quenching capacity (NPQ + NO). In midribs the pattern of quantum yield of regulated energy dissipation (NPQ) was quite similar in all screened leaf areas, and NPQ values remained relatively stable till recovery (day 50), when a significant increase occurred. In contrast, in interveinal areas, NPQ values displayed variability throughout the study and showed some heterogeneity. In fact, NPQ values decreased significantly in a first phase (day 20), and then began to increase until it reached values that were not significantly different from the Fe-sufficient treatment at days 42 and 50. Quantum yield of non-regulated energy dissipation (NO) was enhanced considerably by Fe deprivation, with the highest values in extremely deficient plants. One week after Fe resupply, NO returned to values analogous to those of Fe(+) plants, but II, despite a significant increase in their values, did not recover completely because values of NPQ remained high.
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