LOW SINK-INDUCED STOMATAL CLOSURE ALTERS PHOTOSYNTHETIC RATES OF SOURCE LEAVES IN BEANS AS DEPENDENT ON H_20_2 AND ABA ACCUMULATION IN GUARD CELLS

摘要

Low sink demand provided by pod removal and stem girdling of beans (Vicia faba, cv. Daqingshan) (—Sink) induced a significantly lower net photosynthetic rate (P_n), stomatal conductance (g_s), internal C0_2 concentration (Q), and transpiration rate (E) compared with pod and root sink retention (CK). This depression in P_n was due to stomatal limitation. Low sink demand of—Sink plants resulted in a higher leaf sucrose content, but a lower sucrose content in guard cells. Moreover, the significant accumulation of H_20_2 and ABA were observed in both leaves and guard cells of —Sink plants. The most intensive electron dense deposit of cerium perhydroxides, produced by H_20_2 reaction with cerium chloride, was present in the cell walls, especially thedorsal walls of guard cells. Immunogold electron-microscopy localization of ABA showed that ABA was distributed in ventral walls of guard cells and the intercellular space of mesophyli cells of—Sink leaves in contrast to CK plants. Application of exogenous sucrose to isolated bean leaves increased H_20_2 and ABA contents. H_20_2 and ABA in leaves was likely generated by two independently regulated pathways, each affected by the high sucrose concentration induced by low sink demand. Increased sucrose inleaves in response to low sink demand may have caused the increase of H_20_2 and ABA, and their accumulation in mesophyli cells and guard cells was likely the primary cause for stomatal closure under low sink demand.