Effect of Iron Supply on Growth and Photosystem Ii Efficiency of Pea Plants

Pea plants, grown hydroponically, were supplied with different amounts of iron (Fe) ranging from complete deficiency to toxicity. Plant growth, chlorophyll and carotenoid content and chlorophyll fluorescence parameters were recorded at 7-day intervals from day 20 to day 41. Growth decrease, caused by Fe deficiency or excess as a rule accrued with strengthening and prolongation of the imposed stress. The observed decrease in relative growth rate (RGR’) was mainly due to the decrease of its physiological component, the net assimilation rate. Being only slightly affected, its morphological component, the leaf area ratio (LAR′) was considered as a dynamic component, too. Opposite trends in the changes of is components, leaf weight ratio (LWR) and specific leaf area (SLA), were observed under Fe deficiency. Under partial Fe deficiency RGR′ was high during the last week of the experiment, suggesting that plants had been adapted to insufficient Fe supply. Stresses differed in regard to their effects on SLA, which reflects leaf morphological peculiarities. SLA tended to increase under Fe deficiency and to decrease under excess Fe supply. Fe deficiency was characterized by low pigment content and high chlorophyll a/chlorophyll b and carotenoids/chlorophylls ratios when chlorosis was well manifested. Significant changes in chlorophyll fluorescence were observed only in strongly chlorotic plants. Plants deprived from iron were marked by low actual PS II efficiency (ΦPSII) at days 34 and 41, which was due to lower proportion of open PS II centers (qP) and to their lower excitation capture efficiency (Φexc). The maximum quantum yield of PS II (Fv/Fm) decreased, too. Excess Fe caused rise in pigments content and only slight disturbance in their ratio.