Effect of hydration level in primary bean leaves on the activity of photosystems 1 and 2 in isolated chloroplasts

Pospíšilová J., Zima J., Šesták Z.
BIOLOGIA PLANTARUM 18: 473-479, 1976

Klíčová slova: Hill reaction, quantum efficiency, photochemistry,
Abstrakt: Abstract. Water stress in the leaves was induced by gradual decreasing of substrate moisture in five-day cycles. The hydration level of the leaves was characterized by their water potential (~w), osmotic potential (~Ps), pressure potential (~p), and water saturation deficit (.d W~at). The activities of Photosystems 1 and 2 were determined polarographieally with Pt/Ag(AgOtt) electrode as changes in oxygen concentration in chloroplast suspensions. The shape of light curves of Hill reaction was not influenced by leaf ~w: hence both quantum efficiency and dark phase of this process were affected in a similar manner by water deficit. The activities of both photosystems measured at saturating photon flux density declined with the lowering of leaf ~w (in the range from -5 to -14 • 10 5 Pa) and the decrease in activity of Photosystem 2 was more rapid than that of Photosystem 1. The ratio of activities of Photosystems 1 and 2 was mildly enhanced by a lowering of ~w, but it decreased with increasing age. The lowering of ~w induced lowering in the chlorophyll a/b ratio thus concealing the usual ontogenetic course of this ratio. Additional index words: Phaseolus vulgaris L. ; thermocouple psychrometer.
DOI: 10.1007/BF02922558
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