Stages Of Water Stress Research Articles

Manipulating Panicle Transpiration Resistance to Increase Rice Spikelet Fertility during Flowering Stage Water Stress1

Rice (Oryza sativa L.) is much more sensitive than other cereal crops to drought stress during the flowering period. Anthesis is reduced when the panicle water potential decreases, resulting in largescale spikelet sterility. Improvement of the crop's capacity to flower successfully during water stress will require the improvement of mechanisms to exploit stored soil water or conserve water by reducing transpiration losses from the panicle. Rice panicles typically have very low resistance to water loss even under severe desiccation. This study explored the effects of increased resistance to panicle transpiration as a tactic to maintain high spikelet fertility when anthesis occurs during a drought period. Cultivar IR36 was grown in each of two environments in a phytotron: 1) a glasshouse room with 85% relative humidity (RH), 29/21°C day/night temperatures, and natural light conditions; and 2) Koitotron cabinets (Tokyo, Japan) with 50% RH, 29/21°C day/night temperatures, and natural light conditions. Three water stress treatments were imposed at flowering in each environment by irrigating at a fraction of potential evapotranspiration. Four treatments were applied for 6 days to emerging panicles: Glassine caps open at both ends (GO), or closed at both ends (GC), aluminum foil caps closed at both ends (AC), or no treatment (C). The panicle treatments reduced panicle transpiration rates from 18 to 78% compared to the control. Spikelet temperatures were increased by 1.0 to 2.5°C by the panicle treatments. In the absence of water stress, spikelet fertility was the same for the C, GO, and GC treatments. Under moderate and severe stress in the glasshouse, GO had slightly but not significantly higher spikelet fertility than C. In the Koitotron, all panicle treatments had lower fertility than C when the flowering plants were drought stressed. The panicle treatments decreased transpiration and increased panicle resistance over a substantial range but did not enhance spikelet fertility in the drought stressed treatments. The results indicate that an attempt to improve flowering‐stage drought resistance by breeding morphological changes that increase panicle resistance may not be fruitful.

Reproductive Stage Water Stress and Sterility. I. Effect of Stress during Meiosis1

Increased spikelets sterility is the primary component of yield reduction in rice (Oryzas ativa L.) and other small grains subjected to water stress during reproductive growth stages. The causes of water stress induced spikelet sterility are not clear although the meiotic stage of pollen mother cells is often reported to exhibit yield‐decreasing sensitivity. We exposed rice plants, in which pollen mother cells were actively undergoing meiosis, to the following series of water stress levels as measured by flag leaf water potential: −1.6, −1.9, −2.2, −2.5, −2.8, and −3.5 MPa for 18 to 24 h. Panicles were fixed in Farmer's solution and later examined microscopically for abnormal chromosomal behavior. The occurrence of chromosomal abnormalities such as univalents, lagging of chromosomes, noncongression in metaphase and micronuclei was evaluated in 3822 pollen mother cells in response to increasing water stress levels. Spikelet fertility of comparable panicles grown to maturity decreased linearly from 80% at −1.1 MPa (control) to 50% at −3.5 MPa flag leaf water potential. Chromosomal abnormalities appeared at relatively moderate stress levels (−1.1 to −1.9 MPa) and in general peaked at the −2.2 MPa stress treatment.In general, water stress increased chromosomal abnormalities, except at severe stress levels (−3.5 MPa) where the meiotic process was partially arrested. Each meiotic stage had particular irregularities associated with water stress. Prophase I and II, univalents; Metaphase I, noncongression of bivalents and lagging chromosomes; Anaphase I and II, lagging chromosomes; Telophase II, micronuclei formation. Blasted or immature, small, colorless spikelets also were observed and their occurrence increased with stress level. Blasted spikelets, not included in the calculation of percent sterility, accounted for 10 to 20% of the total spikelets per panicle at moderate stress levels. The cause of this malady is unknown.

Dryland Rice Response to an Irrigation Gradient at Flowering Stage1

AbstractSensitivity of rice (Oryza sativaL.) to flowering stage water stress is well recognized. However, as with other cereals, there is lack of field research which quantifies plant and soil water status at the flowering stage in relation to water stress‐mediated reductions in crop yield. A rice cultivar was subjected to six levels of irrigation using a line‐source sprinkler system in the field on a silty clay loam, Typic Hapludoll soil during the dry season in which a stable rainless period is the climatic norm. Irrigation level 6 (wettest) was irrigated at the rate of 1.10 of pan evaporation while level 1 (driest) relied solely on pre‐line source water storage. Evapotranspiration during the 15‐day treatment period at flowering was linearly related to grain yield. The dominant yield component influencing grain yield was spikelet sterility.At irrigation level 6 in which soil moisture was reduced to 95% of the total crop extractable water, midday leaf water potential was −0.9 MPa, and spikelet sterility was 20%. At level 1, soil moisture was 28.6% of the total crop extractable water, midday leaf water potential −2.5 MPa, and spikelet sterility 73%. The exsertion of the rice panicle was found to be sensitive to changes in leaf water potential. Up to 30% of water stress‐mediated spikelet sterility was associated with poor panicle exsertion. The degree of panicle exsertion during flowering stage water stress may be a useful visual criterion in the selection of breeding lines with high degree of reproductive stage drought resistance.

Water deficits and yield in upland rice

Few data are available relating leaf water potential to yield and yield components. In field conditions, ascertaining leaf water potential at high frequency is both laborious and detrimental to crop stands. Leaf water potential and six soil and climatic descriptors related to the crop water status were monitored in an upland rice farmer's field in the Philippines. Soil matric potential at 15 cm depth and daily total evaporative demand were used to predict daily minimum leaf water potential of the three rice cultivars grown. Difference among rice cultivars for leaf water potential response to soil and atmospheric water status was noted. Establishing −17 bars as a critical leaf water potential allowed determination of degree, duration and degree × duration values of water stress during yield determining growth stages. Results verified the relative lack of yield sensitivity to vegetative stage water stress and the high sensitivity of the reproductive stages. Decreased yield, increased sterility and decreased grain weight were associated with degree and duration of water stress occurring at particular developmental stages.

Net Photosynthesis, Dry Matter Production, and Phenological Development of Apricot Trees (Prunus armeniaca L.) Cultivated in the Negev Highlands (Israel)

Summary Growth rates, phenological development, and daily courses of net photosynthesis were measured on apricot trees ( Prunus armeniaca L.) together with environmental and physiological parameters in the Negev desert under runoff farming conditions. The investigations were conducted during an entire growing period with two experimental trees. One of them received water only from rain and runoff (non-irrigated tree). The other tree was additionally irrigated starting 11 months prior and during the experiments in order to eliminate water stress (irrigated tree). The irrigated tree opened flowers and leaf buds later, also elongation growth started later, but continued for a longer period of time (time of elongation growth months) than in the non-irrigated counterpart (months). Growth was terminated in both trees at a time when predawn water potential reached —7 to —8 bar and daily minimum water potential reached —35 to —40 bar. Trunk growth continued beyond this stage of water stress until the highest water potential in the soil profile reached —10 bar for the non-irrigated and —6 bar for the irrigated tree. The seasonal development of the ratio dry weight/surface area and the ratio chlorophyll/dry weight of the leaves and their anatomy was identical for both trees. The root system was studied intensively for the non-irrigated tree. It had 3 m long tap roots. Horizontal roots were mainly developed in the range of 2 to 3 m, but some lateral roots extended as far as 8 m. The root system exploited a soil volume of about 44—76 m 3 . The root/shoot ratio was 1.1. Because of earlier leaf development, the non-irrigated tree had higher rates of daily CO 2 uptake m spring than the irrigated counterpart, which, in contrast, had higher rates during the dry season. Per unit leaf dry weight the non-irrigated tree had a higher seasonal CO 2 uptake than, the irrigated one (29.5 versus 25.1 gCO 2 • gdw -1 • year -1 ). But because its larger leaf number the irrigated tree achieved an about 30% higher total CO 2 gain per year than its counterpart (about 75 kg C versus 56 kg). The allocation of carbon for leaf, wood, fruit and root growth showed main differences in root and fruit development. It was estimated, that the irrigated tree allocated about 16% (kg C) of its total carbon gain into fruits but only about 13% into roots, whereas the non-irrigated tree allocated% (kg C) of its carbon gain into fruits and about 52% into its below ground parts. The ecological implications of different strategies in growth, photosynthetic production and carbon allocation in trees of differing water stress are discussed.

The Effects of Water Stress on Some Membrane Characteristics of Corn Mitochondria

The effects of water stress on plants have been reviewed in several articles (3, 5-7, 14, 15). These reviews indicated that all plant growth processes are adversely affected at some stage of water stress. Studies of the effects of water stress on subcellular processes are few (1, 4, 13) and cause and effect relationships at this level are little understood. Several recent reports indicate an increase in cytochrome oxidase activity and ultrastructural changes in mitochondria in water-stressed roots under both in vitro and in vivo conditions (12, 13). In studying the reactions of mitochondria isolated from the shoots of water deficient etiolated corn plants, we have noted that the ion and water transport properties of the mitochondria were altered when such properties were compared to mitochondria isolated from the etiolated shoots of nonstressed plants.