Photosynthetic characteristics and chloroplast ultrastructure of wintering oilseed rape under potassium deficiency

Abstract

To understand leaf photosynthesis characteristics and its response to K starvation in oilseed rape,a field experiment was carried out on K- deficient soil with K deficiency(- K) and K supply( + K) treatments.Gas exchange,chlorophyll fluorescence and chloroplast ultrastructure were studied using winter oilseed rape cultivar Zheyou 601 during over- wintering period. Results showed that leaf net photosynthetic rate( Pn) decreased by45. 1% under- K condition. Although stomatal conductance( gs) was lower in- K treatment than in + K treatment,intercellular CO2concentration( Ci) increased 66μmol CO2·mol- 1. Limiting value of stomata( Ls) decreased by 45. 7%. Thus the stomatal factor changes were not the main reason for Pndecrease under – K condition. Further evidences from chlorophyll fluorescence measurement showed that both photosystem II( PSII) maximum photochemical quantum yield( Fv/ Fm) and PSII actual photochemical quantum yield( ΦPSII) were declined under- K treatment,which indicated that PSII reaction center was damaged. In addition,K deficiency affected chloroplast ultrastructure of leaves. In K deficient plants,chloroplast length decreased significantly( with the average of 15. 6%). Chloroplast thickness and distance from chloroplast to cell wall increased by 26. 9% and 56. 1%,respectively. In conclusion,the non- stomatal factors,e. g. damaged PSII reaction center and chloroplast ultrastructure alteration inhibited leaf Pn under K deficiency.