Showing papers by "Rana Munns published in 2000"

Genetic variation for improving the salt tolerance of durum wheat

Abstract: Durum wheat (AB genomes) is more salt-sensitive than bread wheat (ABD genomes), a feature that restricts its expansion into areas with sodic or saline soils. Salt tolerance in bread wheat is linked with a locus on the D genome that results in low Na+ uptake and enhanced K+/Na+ discrimination. In order to introduce salt tolerance into current durum wheats from sources other than the D genome, a search for genetic variation in salt tolerance was made across a wide range of tetraploids representing 5 Triticum turgidum sub-species (durum, carthlicum, turgidum, turanicum, polonicum). Selections were screened for low Na+ uptake and enhanced K+/Na+ discrimination. This was assessed in seedlings grown in 150 mМ NaCl with supplemental Ca2+, by measuring the Na+ and K+ accumulated in the blade of a given leaf over 10 days. Large and repeatable genetic variation was found. Low Na+ accumulation and high K+/Na+ discrimination of similar magnitude to that of bread wheat was found in the sub-species durum. These selections have the potential for improving salt tolerance in durum wheat breeding programs.

Water relations and leaf expansion: importance of time scale

Abstract: The role of leaf water relations in controlling cell expansion in leaves of water-stressed maize and barley depends on time scale. Sudden changes in leaf water status, induced by sudden changes in humidity, light and soil salinity, greatly affect leaf elongation rate, but often only transiently. With sufficiently large changes in salinity, leaf elongation rates are persistently reduced. When plants are kept fully turgid throughout such sudden environmental changes, by placing their roots in a pressure chamber and raising the pressure so that the leaf xylem sap is maintained at atmospheric pressure, both the transient and persistent changes in leaf elongation rate disappear. All these responses show that water relations are responsible for the sudden changes in leaf elongation rate resulting from sudden changes in water stress and putative root signals play no part. However, at a time scale of days, pressurization fails to maintain high rates of leaf elongation of plants in either saline or drying soil, indicating that root signals are overriding water relations effects. In both saline and drying soil, pressurization does raise the growth rate during the light period, but a subsequent decrease during the dark results in no net effect on leaf growth over a 24 h period. When transpirational demand is very high, however, growth-promoting effects of pressurization during the light period outweigh any reductions in the dark, resulting in a net increase in growth of pressurized plants over 24 h. Thus leaf water status can limit leaf expansion rates during periods of high transpiration despite the control exercised by hormonal effects on a 24 h basis.

Rapid environmental changes that affect leaf water status induce transient surges or pauses in leaf expansion rate

Abstract: We subjected wheat and barley plants to rapid environmental changes, and monitored leaf elongation rates for several hours thereafter. Changes in light, humidity or salinity caused sudden rises (if the leaf water status rose) or falls (if the leaf water status fell) in leaf elongation rate, followed by a recovery phase that lasted 20–60 min. After a step change in light or humidity, the growing leaf eventually resumed its original elongation rate, although the shoot water status, as monitored by leaf thickness, differed markedly. Salinity, on the other hand, produced a persistent change in leaf elongation rate, which settled down to a lower steady rate after the transient response was over. To determine whether the sudden changes in leaf elongation rate were due to changes in leaf water relations, we kept shoots fully hydrated through the environmental changes by automatically pressurising the roots to maintain leaf xylem on the point of bleeding. This annulled the environmental effects on leaf water status, and thereby largely removed the changes in leaf elongation rate. The only exception was at the dark:light transition, when the leaf elongation rate of pressurised plants rose sharply (in contrast to that of unpressurised plants, which fell), then underwent damped oscillations before settling at about its initial value. The sudden excursions of leaf growth in unpressurised plants accompanying the environmental changes were undoubtedly due to changes in leaf water status. The subsequent, generally complete, return of the leaf elongation rate to its initial value within an hour, despite the persistent change in leaf water status, suggests that a control system is operating at a time scale of tens of minutes that eventually overrides, partially or completely, the rapid effects of changes in leaf water status.

Leaf water status controls day-time but not daily rates of leaf expansion in salt-treated barley

Abstract: Barley plants were grown in pots that would fit inside a pressure chamber, so that their shoots could be kept fully turgid by applying pressure in the chamber to bring the xylem sap of the shoot to the point of bleeding. Pressurisation increased the growth rate of NaCl-treated plants in the light period but not in the dark. The promotive effect on growth was greatest in the light period of the first day of pressurisation, but disappeared during the first night. Pressurisation promoted growth the next day during the light period, but on the second night the elongation rate was significantly lower than that of unpressurised NaCl-treated plants. This pattern of high day-time and low night-time growth then continued indefinitely. The lower night-time growth counteracted the higher day-time growth, with the result that total growth over 24 h was the same as in NaCl-treated plants that were not pressurised. Levels of total reserve carbohydrates were unaffected by pressurisation, indicating that the slower growth of the pres-surised plants during the night was not due to depletion of assimilates. These results are interpreted in the context of hormonal signals controlling growth on a 24-h basis, such that any short-term stimulation of growth arising from unusually high water status during the light period is counterbalanced by slower growth during the night.

Yellow lupin (Lupinus luteus) tolerates waterlogging better than narrow-leafed lupin (L. angustifolius). IV. Root genotype is more important than shoot genotype.

Abstract: To understand how yellow lupin tolerates waterlogging better than narrow-leafed lupin, we investigated the roles of the roots and the shoots of these species. Reciprocal- and self-grafted combinations (scion = shoot/rootstock) of yellow and narrow-leafed lupin were made at the 2-leaf stage and waterlogged 45 days later (8–10 leaf stage). Responses to waterlogging were examined at the end of waterlogging and following a recovery period of 14 days.Waterlogging of reciprocal and self-grafted plants reduced total plant dry weight by 15–58% compared with non-waterlogged controls. These reductions were greater when the rootstock was narrow-leafed rather than yellow lupin, and were similar for the roots and shoots. Waterlogging increased dry weight of hypocotyl roots in most grafting combinations (by 2–19-fold), but grafts with narrow-leafed lupin scions produced almost twice the hypocotyl root length of grafts with yellow lupin scions. During the waterlogging period, leaf gas exchange decreased by 16–74% in all grafting combinations except in narrow-leafed lupin scion/yellow lupin rootstock where it increased by 17–30%. During waterlogging, stem water potential decreased and leaf osmotic pressure increased. These changes compensated one another and consequently there was no effect on bulk leaf turgor. After 14 days recovery, water relations returned to initial values. Tolerance of the whole plant to waterlogging was influenced more by the root genotype than the shoot genotype. However, production of hypocotyl roots in response to waterlogging was related to the shoot genotype rather than the root genotype.