Vergara - 1976 - Physiological and morphological adaptability of ri

342 CLINLATE AND RICE
ALLURI: Could the lower effect on translocation be due to the small amount of water that
was added on alternate day's’?
Bqtter: “It: measured leaf yvatcr potential on these days and lhund that it changed by only
about 2 bars as a result of watering (water was always added at the beginning of the day). Thus.
photosynthesis remained highly inhibited but translocation continued. Consequently’. the
difference in sensitivity ofthcsc processes appears valid. cvcn if the translocation was most rapid
afier the slight rewatering.
ALLBSI I recall reading in the literature about some experiments on the use of certain longchain
alcohols (Octadecanol) applied to the root zone, as a means of minimizing moisture loss
from leaves. Do you think that in addition to the breeding approach to drought resistance. this
or other agronomic practices would be usefiil in mitigating ivater deficits?
On the other hand. do heavy fertilization and consequent luxuriant growth result in a
plant becoming more prone to water deficits‘?
Boyer‘: The subsequent research with long-chain alcohols showed that their long-term toxic
effects tend to outweigh the short-term beneficial effects. Ilowevcr. in principle. substances
that slow down water loss might have agricultural usefulness. ?erhaps one of the largest problems
even with successful transpiration suppressants is their tendency to inhibit photosynthesis.
Consequently". a good deal of sophistication is required to know exactly when they"
should be used.
The interaction between soil lertilitf; and drought eficcts is complex. but from What I can tell,
the literature suggests that high fertility frequently is associated with a high percentage of yield
loss during drought. Since high fertility" often results in generally higher yields. however, more
yield can be sacrificed during drought without losing the benefits of high fertilizer applications.
ORA: How" do you measure “leaf water potential"?
Boyer: ‘We use the pressure chamber and the isopicstic thcnnocouple psychromctcr. The
former is particularly useful in the licld, whereas the latter is primarily a laboratory instrument.
PAcARDci; What would be the reason that zero water potential was not obtained as a result
of night recovery’ in well-yvatcred plants?
Bqveiz- We have evidence that the low water potentials (—l to —2 bars instead of zero) are
associated with waster uptake for grovrth. In nongrowing or slowly growing tissues, water
potentials arc considerably closer to zero. In most cases. the —l to —2 bar water potentials
appear to be present in the intact plants.
h-IANUEL: l. Water potential changes seem to be rapid responses to light or to temperature.
ls there no time lag observed between their inception and the perception of the stimulus’?
2. Do these changes exhibit any regular rhythmicity"?
3. Reports have been made on the improvement of drought resistance in plants through the
application of growth retardants and anti-transpirants. Do these chemicals have any direct
effects on the water potentials of the cells‘?
Boyer: l. "Fherc is a lag associated with the decline in water potential, the size of which
depends on the difference in the rate of water uptake and water loss by the tissue and the bulk
of the tissue.
2. There is rhythmicity' caused by the natural rhythmicity’ of the evaporative and radiational
enviromnent. We have not tested whether there is an endogenous rhythm.
3. These substances frequently alfcct the water potentials of the cells largely through their
effects on the rate of water loss from the leaves.
DE DATE-x: 1. How" do you quantify desiccation to detemiine leaf-water potential at different
growth stages?
2. If desiccation is a reversible process. should we pay more attention to the recovery from
drought than to drought tolerance per s2? Of course we need both factors.
Our studies on rice indicate that it can tolerate gradual increase of soil-water potential up to
l5 bars.
3. As a comment. I am glad you emphasized that yield-determining factors should be considered
in screening for drought tolerance.
BQi-‘er: l. We measure leaf water potentials directly and frequently measure soil-water potentials
as well. The only other character which we use is the time for development of water
deficits, since effects may vary with the rate of onset of drought.