Al. Nepomuceno et al., PHYSIOLOGICAL-RESPONSES OF COTTON LEAVES AND ROOTS TO WATER-DEFICIT INDUCED BY POLYETHYLENE-GLYCOL, Environmental and experimental botany, 40(1), 1998, pp. 29-41
The characterization of plant water relations is a prerequisite for su
bsequent selection and genetic manipulation for drought tolerance. To
evaluate roots in addition to leaves, a method based on PEG was develo
ped to obtain clean, stressed roots quickly while avoiding toxic effec
ts associated with PEG treatment. A mild water deficit of - 0.3 MPa wa
s induced with polyethylene glycol (PEG 6000) around the roots of four
cotton (Gossypium hirsutum) genotypes with different water deficit to
lerances. Treatment with PEG during diurnal dark period avoided toxic
effects observed with treatment during the light period. The genotypes
examined included: (1) Siokra L-23, a drought-tolerant cultivar; (2)
T-1521, a wild-type with significant osmotic adjustment capability; (3
) CS-50, a moderately susceptible cultivar; and (4) Stoneville 506, a
susceptible cultivar. The water potentials (psi(w)) and osmotic potent
ials (psi(s)) of roots and leaves of stressed and nan-stressed plants
were determined psychrometrically. In response to the water deficits S
iokra L-23 and T-1521 showed 25 and 20% reductions in leaf psi(s),, re
spectively, compared with unstressed controls. At the same time, psi(w
) of these two genotypes did not change significantly. Conversely, the
decrease in the psi(s) of CS-50 and Stoneville 506 was not significan
t, while their psi(w) decreased significantly. By maintaining a higher
psi(w) during stress, the tolerant genotypes were able to maintain ph
otosynthesis, stomatal conductance and relative water content near uns
tressed control levels. The use of PEG 6000 to maintain a constant psi
(w) in the root environment provides an efficient method for controlli
ng psi(w) while allowing for rapid sampling of clean root tissue for a
nalysis. The results demonstrated that the empirically determined diff
erences in drought tolerance of these cultivars can be related to meas
urable physiological parameters. These results suggest that physiologi
cal monitoring can be an effective tool in germplasm selection and imp
rovement. (C) 1998 Elsevier Science B.V. All rights reserved.