One of paired tomato plants was sprayed with 100 ppm phenylmurcuric acetate (PMA). Transpiration rates were measured gravimetrically. During the initial daylight periods, PMA treatment reduced water losses in 2 tests. Conversely, night water losses were higher for the PMA treated plants in both tests. When moisture stress symptoms occurred, water losses by the treated plant were higher. The results indicate that PMA closes the stomates at some small aperature. This reduces transpiration when plants are not stressed for water. Relative increased water losses occur, however, when untreated plant losses would be minimal (dark, wilted).
Rambutan (Nephelium lappaceum L.) rapidly lose their attractive appearance after harvest due to a superficial pericarp browning. Storage at high humidity minimizes fruit desiccation and may, therefore, delay browning onset. This paper examines the effect of reduced water loss rate on browning that may occur with time. Rambutan fruit pericarp browning beyond a commercially saleable level occurred at a weight loss of 25% to 40%. This depended on duration and storage relative humidity (RH). Skin browning was 50% greater on the red (R 134) than the yellow (R 156) cultivar at 60% RH. There was a storage time × RH interaction in the development of browning such that browning was observed earlier at lower RHs. Skin browning and spintern (soft spine) browning developed independently. Cracks appeared on the surface of fruit with increased weight loss. Browning occurrence was consistent with increased total phenolic compound levels in the pericarp. Water loss precedes browning occurrence and, over time, water loss is related to browning. Water stress appeared to affect rambutan pericarp tissue in much the same manner as senescence.
Scanning electron microscopy was used to investigate leaf epicuticular wax of Prunus instititia L. ‘Pixie’ from aseptically cultured plants before and after acclimatization to the greenhouse. Leaves from plants acclimatized for 2 weeks in the greenhouse had more adaxial wax than those from non-acclimatized (culture flask-grown) plants. Acclimatized plants had more adaxial than abaxial wax. No abaxial wax was observed on leaves of non-acclimatized plants. Stomata were present on the abaxial leaf surface only of both acclimatized and non-acclimatized plants. Epicuticular wax layers surrounded guard cells of acclimatized plant leaves but were not present on non-acclimatized plant leaves. Weight changes in non-acclimatized plant leaves coated with silicon rubber on adaxial, abaxial, and both surfaces indicated that excised leaf water loss occurred only through the abaxial surface. Water loss from plants during the acclimatization process thus may be due to abaxial cuticular and stomatal transpiration.
Foliar anatomical comparisons were made between in vitro-grown plantlets and greenhouse-grown plants of ‘Silvan’ blackberry (Rubus sp.) using scanning and light microscopy. Each apex and marginal serration of in vitro- and greenhouse-grown leaves had a terminal hydathode region composed of a scattered, primarily adaxial, group of sunken water pores. Water pores and stomata of plantlet leaves were open, while greenhouse-grown plant leaves had closed water pores and stomata or comparatively small apertures. Internally, the hydathodes of both cultured plantlets and greenhouse-grown plants were delimited by a bundle sheath that flanked the vascular tissues and extended to the epidermis. Between the vascular tissues and the epidermis were loosely arranged epithem cells. The hydathodes of plantlet leaves were simpler than those of greenhouse-grown plants, with fewer water pores and reduced epithem. Water loss from detached leaves of plantlets occurred through both leaf surfaces, although more water was lost from the abaxial surface. In contrast, foliar water loss from severed leaf blades of greenhouse-grown plants was primarily abaxial.
Measurements of global radiation above, and net solar radiation below, the roof of a glasshouse were both highly correlated on a daily and hourly basis with the water loss from a flowering rose crop as measured with a weighing lysimeter. The relationship can be used for an automatic system of irrigation control. Under local glasshouse, soil, and crop response conditions such a system would require an application of 6 liters of water per square meter of bed for every 730 cal cm2 global radiation above the glasshouse. Alternatively, a foliage spray irrigation system to ensure that the upper part of the canopy is kept continuously moist, would require applications of at least 0.4 liters per square meter at radiation intervals between 15 and 4 cal cm2 of global radiation outside the greenhouse, the exact figure depending mainly on the rate of air movement around the foliage. The latent heat equivalent of the crop water loss was 87% of the global radiation incident on the canopy, a figure similar to those listed for other, tall glasshouse crops.
Six commercial cultivars (Anna, Aurore, Danhill, Danlight, Melanie, and Thelca), one drought tolerant cultivar (Orangeade), nine breeding selections, and one check genotype of Impatiens hawkeri Bull were evaluated for differences in drought tolerance based on water loss and time to wilt. The six commercially available cultivars had significantly higher mean water loss than the breeding selections and `Orangeade'. These cultivars wilted in 5.11 vs. 7.33 days for `Orangeade' and 9.10 days for the breeding selections. These results suggest that sufficient variability exists in New Guinea impatiens germplasm for the reduction of water loss to improve drought tolerance. Regression analysis revealed that total transpirational water loss 96 hours after withholding water was an excellent predictor of the time to wilting (a simple measure of drought tolerance) after water was withheld (R2 = 0.95). Thus, a simple, efficient and objective method for selection of drought tolerant genotypes has been developed for New Guinea impatiens. A comparison of offspring to parental genotypes showed that after only one cycle of selection, water loss was significantly reduced by >30%. These results suggest that there is sufficient genetic variability present for the development of more drought tolerant cultivars.
Water loss was found to be a nondestructive indicator before visible symptoms of chilling injury (CI) in cold-stored grapefruit (Citrus paradisi Macf.) and lemon (C. limon L. Burm. f.). The water-loss rate increased significantly after removing the fruit from cold storage and holding at 20C. Scanning electron microscopy revealed large cracks around the stomata. Changes in electrical conductivity of the flavedo tissues, total electrolyte leakage, and K+ or Ca2+ leakage were all inadequate predictors of CI, appearing only after CI was evident.
Fruit of pepper (Capsicum annuum L.) is hollow by nature, which limits its water reservoir capacity, and as such, small amounts of water loss result in loss of freshness and firmness, which reduce fruit quality, shelf life, and market value. In order to understand the basis for water loss from fruit, 10 pepper accessions with wide variation in water loss rate were used to study physiological and biochemical factors associated with postharvest water loss in ripe pepper fruit during storage. Postharvest water loss rate in ripe pepper fruit stored at 20 °C, and 85% relative humidity, was found to be associated with cell membrane ion leakage, lipoxygenase activity, and total cuticular wax amount. Total cuticular wax amounts were highest in the high-water-loss pepper fruit, and lowest in the low-water-loss fruit. However, total cuticle amount (isolated enzymatically and quantified gravimetrically), total cutin monomer amount, and the amount of individual cutin monomer and wax constituents (determined using gas chromatography mass spectrometry) indicated no direct association with postharvest water loss rates. Fruit fresh weight, pericarp weight, pericarp surface area, pericarp thickness, initial water content, and dry matter were highly associated with each other, but less so with water loss rate. Fruit of accessions displaying high fruit water loss rate matured and ripened earlier than fruit of accessions displaying low-water-loss rate. Cell membrane ion leakage and lipoxygenase activity were higher after storage than immediately after harvest. Pepper fruit total cuticle wax amount, lipoxygenase activity, and cell membrane ion leakage were directly related to postharvest water loss rate in pepper fruit during storage.
A foliar application of 5 × 10−5 M phenylmercuric acetate plus a wetting agent reduced water loss by transpiration from chrysanthemum plants by more than 30% for a period of 4 days following treatment without causing tissue damage or inhibiting growth and flowering. This reduction of transpiration was associated with a reduction of stomatal pore size. However, treatment concentration was critical, as foliar damage and reduction in growth occurred at high concentrations of PMA.
Several film forming antitranspirants were applied to salable, flowering chrysanthemum plants prior to placement in a controlled environment devised to simulate the interior of a home. Significant reductions in water loss resulted with all applications, with over a 40% reduction at highest concentrations. No discernable increase in floral display life was observed with any treatment. Higher concentrations of chemicals caused yellowing of foliage, and in some cases imparted a sticky residue or in some way impeded normal floral expansion. Film effectiveness persisted for at least 2 weeks with consistantly high transpiration losses for non-treated plants.