CORRELATION BETWEEN THE INHIBITION OF PHOTOSYNTHESIS AND THE DECREASEIN AREA OF DETACHED LEAF DISCS OR VOLUME ABSORBANCE OF PROTOPLASTS UNDER OSMOTIC-STRESS IN PEA (PISUM-SATIVUM)/
K. Saradadevi et al., CORRELATION BETWEEN THE INHIBITION OF PHOTOSYNTHESIS AND THE DECREASEIN AREA OF DETACHED LEAF DISCS OR VOLUME ABSORBANCE OF PROTOPLASTS UNDER OSMOTIC-STRESS IN PEA (PISUM-SATIVUM)/, Physiologia Plantarum, 96(3), 1996, pp. 395-400
Exposure to osmotic stress reduces leaf area and protoplast volume whi
le decreasing photosynthesis. But the measurement of protoplast volume
is tedious, while rapid determinations of leaf area in the field are
difficult. We evaluated the quantitative relationship between the exte
nt of decrease in area of detached leaf discs or the volume of protopl
ast of pea (Pisum sativum) and reduction in their photosynthetic capac
ity under osmotic stress. Osmotic stress was induced by increasing sor
bitol concentration in the surrounding medium of the leaf discs from z
ero to 1.0 M (-3.1 MPa), and in case of protoplasts from 0.4 M (-1.3 M
Pa, isotonicity) to 1.0 M (-3.1 MPa, hypertonicity). There was a high
degree of positive correlation between the extent of reduction in the
area of detached leaf discs or the volume of protoplasts (indicated by
diameter or absorption at 440 nm) and the decrease in photosynthesis.
The correlation coefficients between inhibition of photosynthesis and
the decrease in leaf disc area or protoplast volume were 0.96 and 0.9
9, respectively. We therefore suggest that the decrease in absorbance
at 440 nm (corrected for turbidity at 750 nm) can be used as a simple
measure to predict the inhibition due to osmotic stress of photosynthe
sis in mesophyll protoplasts. Similarly, the reduction in area of deta
ched leaf discs could also be a very simple and useful criterion to as
sess osmotic tolerance of photosynthesis.