Postharvest Biology and Technology 21 2001 179 – 188
Phosphorus status affects postharvest respiration, membrane permeability and lipid chemistry of European seedless
cucumber fruit Cucumis sati6us L.
L. Knowles, M. Rae Trimble
1
, N. Richard Knowles
Department of Horticulture and Landscape Architecture, Washington State Uni6ersity, Pullman, WA
99164
, USA Received 28 January 2000; accepted 30 June 2000
Abstract
Fruit of European seedless cucumber were grown in a greenhouse under low and high phosphorus P fertilization regimes. Tissue P concentration of fruit number one grade from low-P plants was, on average, 45 of that of fruit
from high-P plants. Fruit P status affected membrane lipid chemistry and fruit respiration after harvest. Mesocarp tissue of low-P fruit had a lower concentration of phospholipids, lower level of unsaturation in various pools of fatty
acids, and a greater rate of electrolyte leakage than that of high-P fruit. On average, respiration of low-P fruit was 21 higher than that of high-P fruit over a 16-day postharvest interval at 23°C. Moreover, low-P fruit experienced
a climacteric in respiration that began about 40 h after harvest, reached a maximum at 72 h, and declined to preclimacteric levels by 90 h. The difference in respiration rate between low- and high-P fruit was as high as 57
during the climacteric. The respiratory climacteric was unique to the low-P fruit and was not associated with an increase in fruit ethylene concentration or ripening. Phosphorus nutrition can thus alter the postharvest physiology
of cucumber fruit by affecting membrane lipid chemistry, membrane integrity and respiratory metabolism. © 2001 Elsevier Science B.V. All rights reserved.
Keywords
:
Cucumis sati6us; Phosphorus nutrition; Postharvest respiration; Membrane lipids; Electrolyte leakage www.elsevier.comlocatepostharvbio
1. Introduction
The effects of phosphorus P nutrition on crop growth rate and fruit P content of greenhouse-
grown, European seedless cucumber Cucumis sa- ti6us L. are well established Trimble and
Knowles, 1995a,b. However, studies on the ef- fects of P nutrition on the postharvest physiology
of cucumber and other fruits are rare, with most of the research focussed on pome fruits. Phospho-
rus nutrition has been shown to affect fruit firm- ness and the occurrence of low-temperature
breakdown in apples Sharples, 1980. Foliar ap- plications of P during the growing season in-
creased tissue P concentration and reduced the
Corresponding author. Tel.: + 1-509-3353451; fax: + 1- 509-3356890.
E-mail address
:
rknowleswsu.edu N.R. Knowles.
1
Present address: ICMS, Inc., P.O. Box 67, Highway 1A East, Portage la Prairie, Manitoba, Canada R1N 3B2
0925-521401 - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S0925-52140000144-7
incidence of storage disorders in apple Yogarant- nam and Sharples, 1982. Lin and Ehret 1991
showed that the shelf-life of greenhouse cucumber cv. Mustang could be improved by increasing
the concentrations of N, P, K, Ca, S and Mg in the nutrient solution, but it was not possible to
isolate a specific effect due to P from their data.
The effect of P on the postharvest physiology of fruit may be attributed to its role as a component
of phospholipids, a major constituent of cell membranes. Alterations in membrane composi-
tion occur naturally during fruit ripening and senescence and are also a mechanism by which
cells adapt to changing environmental conditions. For example, phospholipid content increased in
apple during storage at 0°C, purportedly as an adaptation to maintain membrane function at this
low temperature Lurie et al., 1987. Phosphorus deficient plant organs may be unable to make this
adaptation. It is commonly observed in fruit tis- sue that membrane function declines with ripen-
ing and senescence, and this occurs concomitant with a loss of phospholipids andor changes in
their constituent fatty acids. The most frequently reported change in fatty acid chemistry is an
increase in saturation at the expense of unsatura- tion Lurie and Ben-Arie, 1983; Lester and Stein,
1993; Palma et al., 1995; Rogiers et al., 1998a.
A few studies have indicated that P content can potentially affect the postharvest respiration rate
of fruit, which is often inversely related to storage and shelf-life Kader, 1987. Letham 1969 found
that higher levels of P fertilization resulted in higher P concentration in apple and that fruit P
content was negatively correlated with respiration rate. Another study of respiration in apple found
no relation between tissue P concentration and respiration rate Davenport and Peryea, 1989. In
this latter study, differences in tissue P were due to natural variation among fruits and the applica-
tion of CaCl
2
sprays, and were not as great as those induced by varied P nutrition.
Despite inconsistencies in the literature, it is evident that plant P nutrition affects fruit P status
and this in turn may have a significant influence on postharvest physiology and thus storability
and shelf-life of fruit. The experiments described herein were designed to induce differences in P
concentration of European seedless cucumber fruit so that the effects of fruit P-status on respi-
ration rate, membrane lipid chemistry and mem- brane function could be assessed after harvest.
2. Materials and methods
