flowers, including carnations, are the result of stomatal waterloss that gradually exceeds the rate of water uptake through the xylem vessels in the cut-stem ends ( Mattos et al., 2017 ; van Doorn, 2012 ). The stomata of higher plants occur mainly on the
Termination of vase life for cut flowers is characterized by wilting associated with an imbalance developing between water uptake through xylem conduits in stems and waterloss through stomata and other structures on leaves and other organs. To
Transpiration rates of chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] plants grown under spectral filters were evaluated as part of an investigation on using light quality to regulate plant growth. The 6% CuSO4·5H2O spectral filter reduced photosynthetic photon flux density in red (R) and far red (FR) wavelengths and increased the R: FR and blue (B): R ratios (B = 400 to 500 nm; R = 600 to 700 nm; FR = 700 to 800 nm) of transmitted light relative to the water (control) filter. After 28 days, cumulative water use of plants grown under CuSO4 filters was ≈37% less than that of control plants. Transpiration rates were similar among plants grown under CuSO4 and control filters when expressed as leaf area, a result suggesting that the reduced cumulative water loss was a result of smaller plant size. Plants grown under CuSO4 filters had slightly lower (10%) stomatal density than control plants. Light transmitted through CuSO4 filters did not alter the size of individual stomata; however, total number of stomata and total stomatal pore area per plant was ≈50% less in plants grown under CuSO4 filters than in those grown under control filters due to less leaf area. The results suggest that altering light quality may help reduce water use and fertilizer demands while controlling growth during greenhouse production.
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).
Freeze-damaged ‘Marsh’ grapefruit (Citrus paradisi Macf.) and ‘Pineapple’ orange [Citrus sinensis (L.) Osbeck] fruit were sealed in polyethylene shrink film and stored for 6 weeks at 15°C in an attempt to prevent segment dehydration. Although the film greatly restricted water loss from the fruit, segment dehydration was similar to that observed for waxed fruit. During dehydration of freeze-damaged segments of ‘Valencia’ orange fruit, the relative water content of the adjacent mesocarp tissue increased. However, no differences were found in the soluble carbohydrate levels in mesocarp tissue adjacent to damaged and undamaged segments. The results indicate that the mesocarp tissue is not only in the pathway of water loss from free-damaged citrus fruit, but also accumulates water from damaged tissues. Furthermore, segment tissue membranes and walls appear to be differentially permeable to sugars and water.
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.
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.
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.