In unstressed apple seedlings (Malus domestics Borkh.), concentrations of free abscisic acid (ABA) decreased in order from apical stem sections, immature expanding leaves, mature stem sections, and mature leaves. PEG-induced water stress stimulated a 2- to 10-fold increase in free ABA concentrations 1 day after treatment, depending on the amount of stress and the tissue. By the 3rd day of stress, free ABA concentrations were nearly the same as the unstressed treatment and remained low for the remainder of the 21-day stress period. Bound ABA concentrations were an order of magnitude lower than free ABA and were not influenced dramatically by water stress. Shoot growth rate, leaf expansion rate, and leaf emergence rate were reduced by water stress in relation to the severity of the stress; this reduction was associated with the initial increase in ABA. However, there was no increase in shoot or leaf growth rates associated with the decline in ABA concentrations by day 3 as growth rates remained depressed on water-stressed plants throughout the 21-day stress period. Water stress reduced evapotranspiration rate and midshoot leaf water potential (ψW)after 1 day, but leaf osmotic potential (ψS) adjusted more slowly, resulting in a loss of leaf turgor. The reduction in leaf turgor pressure (ψP) was highly correlated with decreased shoot growth rate and increased ABA concentrations on day 1 after treatment. By the 3rd day of water stress, ψP bad recovered even in the most severe treatment, and the recovery of turgor was associated with the drop in ABA concentrations. However, the increase in midshoot ψP and the decline in ABA were not associated with any increase in shoot growth rate. The continued inhibition of shoot growth was probably not related to ABA or turgor pressure of mature leaves but may have been related to turgor pressure in the growing tip.
Water uptake by impatiens (Impatiens wallerana Hook. f. cv. Super Elfin Coral) seeds was measured as an increase in fresh weight every 24 hours during 144 hours of germination. Seeds absorbed most of the water required for germination within 3 hours of imbibition and germinated at 60% to 67% moisture on a dry-weight basis. Germination started at 48 hours and was complete by 96 hours at 25C. Water stress of -0.1, -0.2, -0.4, and -0.6 MPa, induced by polyethylene glycol 8000, reduced germination by 13%, 49%, 91%, and 100%, respectively, at 96 hours. Under the same water-stress conditions, increases in fresh weight were inhibited by 53%, 89%, 107%, and 106%, respectively. Three distinct groups of storage proteins were present in dry seed; their estimated molecular weights were 1) 35, 33, and 31 kDa; 2) 26, 23, and 21 kDa; and 3) two bands <14 kDa. Major depletion of storage proteins coincided with the completion of germination. Water potentials that inhibited germination also inhibited degradation of storage proteins. During germination under optimum conditions, the soluble protein fraction increased, coinciding with a decrease in the insoluble fraction.
An undergraduate class in postharvest physiology observed a number of factors in the senescence of cut roses, which had been studied separately in the literature. They assessed the relative importance of the factors in determining vase life. `Samantha' roses were held at 20C in distilled water or a floral preservative. Ethylene treatment caused petal distortion and premature senescence. Floral preservatives stimulated ethylene production, although vase life was extended relative to flowers in water. Higher sugar contents and respiration were maintained in preservative than in water. Water uptake by roses was almost constant, but stem resistance to water flow increased faster in water than in preservative. In the 2nd week of vase life, transpiration exceeded water uptake, particularly for roses in water. As much of this water was lost through leaves as through the flower. The results suggest that a complex interaction of several factors determines vase life.
-watered conditions, in which seedlings were growing in half-strength Hoagland solution and 2) PEG-induced drought conditions, in which seedlings were growing in half-strength Hoagland solution plus PEG 6000 (30%; Beijing Kebaiao, Beijing, China). Water potential of
screen potential resistant resources for kiwifruit breeding or rootstock selection in future studies, the growth and physiological responses of five Actinidia species to PEG-induced drought stress under tissue culture conditions were measured, and the
Abbreviations: PEG, polyethylene glycol; PER, peroxidase; PGI, phosphoglucose isomerase; PGM, phosphoglucomutase. Florida Agricultural Experiment Station Journal Series no. R-01587. We thank X.B. Ling, S. Huang, D.C. Chen, and N. Tusa for technical
Abbreviations: EPM, embryo production medium; GABA, γ -aminobutyrate; PEG, polyethylene glycol. Journal paper no. 12,637 of the Purdue Univ. Agricultural Experiment Station. We thank A. Altman, Faculty of Agriculture, Hebrew Univ. of Jerusalem, for
beginning of the 20% polyethylene glycol treatment to allow the plants to reach full maturity and develop uniform and equal size roots and shoots. Treatment and experimental design. After adaptation, the plants were exposed to 20% PEG 6000 (−1.8 MPa) for 2
(hydropriming) and PEG (osmopriming) increased germination rate and quality of seedling ( Kamau and Maina, 2017 ; Pill and Kilian, 2000 ), whereas parsley seeds treated with GA using Progibb Plus 2X (Abbott Laboratories, Chicago, IL) as a priming agent
-priming using GB ( Pill and Necker, 2001 ; Zhang and Rue, 2012 ; Zhang et al., 2014 ) and PEG ( Danneberger et al., 1992 ; Wang et al., 2014 ), matrix priming ( Yamamoto et al., 1997b ), and redox priming using H 2 O 2 ( Wang et al., 2014 ) have been