Moshe Huberman

Probing the role of endogenous ethylene in the degreening of citrus fruit with ethylene antagonists

The ethylene antagonists, 2,5-norbornadiene (NBD) and silver nitrate, were used to probe the involvement of endogenous ethylene in the natural degreening of citrus fruit. Mature-green, detached ‘Shamouti’ orange (Citrus sinensis L. Osbeck) fruit were treated with NBD vapor or dipped in solutions of silver nitrate. More than 80% of the chlorophyll was lost from control fruit after 8 days. NBD (0.11 mmole/liter) inhibited the loss of chlorophyll by 60%. NBD also antagonized the degreening induced by exogenous ethylene by 50%. Silver nitrate (0.1 mM) inhibited the loss of chlorophyll by 55%. Ethylene evolution of mature, green detached fruit was <2 nl.fruit-1.h-1 (ca. 13.5 nl.Kg-1FW.h-1) and did not change significantly for 7 days after harvest. NBD concentrations up to 0.22 mmole/liter did not enhance ethylene evolution. Not with-standing the extremely low amounts of ethylene evolved, the inhibition of degreening by NBD and silver nitrate suggests that endogenous ethylene is involved in the control of this process in mature citrus fruit.

Role of Ethylene Biosynthesis and Auxin Content and Transport in High Temperature-Induced Abscission of Pepper Reproductive Organs

Abstract. High temperatures induced abscission of pepper (Capsicum annuum L. cv. Maor) reproductive organs at various developmental stages. The role of ethylene biosynthesis and auxin economy in high temperature-induced abscission is described. High temperatures somewhat increased ethylene production in the reproductive organs, but the highest temperature treatment, which was the most active in inducing reproductive organ abscission, decreased it. In contrast to ethylene, 1-aminocyclopropane-1-carboxylic acid levels increased significantly in response to high temperatures and correlated positively with the increase in temperature. High temperatures reduced indole-3-acetic acid levels and particularly auxin transport capacity in the reproductive organs. The data suggest that the reduction of auxin transport capacity is the major mechanism by which high temperatures induce reproductive organ abscission in pepper.

A simple and sensitive staining method for the detection of cellulase isozymes in polyacrylamide gels

Abstract A simple and rapid staining procedure is described for qualitative and quantitative determination of the activity of plant ( Citrus sinensis (L.) Osbeck cv. Shamouti) and fungal ( Trichodermata viride ) cellulases in polyacrylamide gels. The method is based on the incorporation of carboxymethyl cellulose, a cellulase substrate, into the gels. After electrophoresis of crude extracts the gels are incubated in sodium-potassium phosphate buffer for the cellulase reaction which is stopped at the desired time by acidification of the gels in 60% sulfuric acid. The gels are then exposed to 2.0% KI + 0.2% I 2 . No color develops in areas containing cellulase activity. The experimental procedure is described, and its different aspects are discussed.

Effect of 3-cyclopropyl-1-enlyl-propanoic acid sodium salt, a novel water soluble antagonist of ethylene action, on plant responses to ethylene

A novel water soluble inhibitor of ethylene action, 3-cyclopropyl-1-enyl-propanoic acid sodium salt [(CPAS) Patent Application number: PCT/IL2008/000995, US Application number 61/144758, International publication number: WO 2009/010981 AI] was synthesized in a highly purified form, and its effect to retard various exogenous or endogenous ethylene-mediated processes was tested. The inhibitor was applied by loading, dipping or spraying. CPAS retarded some ripening processes in avocado, banana, and peach fruit, delayed abscission of citrus leaf explants, inhibited leaf epinasty in tomato seedlings, and prolonged the vase-life of carnation and petunia flowers. The fact that CPAS is a solid, water soluble, non-phytotoxic, and odorless inhibitor of ethylene action renders it a promising candidate for pre- and post-harvest application in a wide rang of open growing environments.

In vitro sugar uptake by grapefruit (Citrus paradisi) juice-sac cells

To further our understanding of the mechanisms of sugar uptake and accumulation into grapefruit (Citrus paradisi Macf. cv. Marsh seedless), the patterns of uptake and utilisation of sucrose, glucose and fructose by Citrus juice cells was investigated. Analyses were conducted on sliced juice sacs that were incubated in radioactive [14C]-sugar solutions with unlabelled sugars, in the presence or absence of metabolic inhibitors. Both hexoses demonstrated an initial uptake peak in December and a second uptake peak in February-March. From March through April the rates of sucrose uptake increased to levels comparable to those of glucose and fructose. Sucrose and its moieties fructose and glucose entered the juice cells of Citrus juice fruit by an insaturable, and mostly by an independent, process. However, NaN3 and carbonylcyanide m-chlorophenylhydrazone (CCCP) produced slight inhibition of these processes. Cells took up hexoses at a greater rate than sucrose, with accumulation reaching a plateau by 4-8 h, and then continuing unabated, in the case of glucose, for 42 h. Uptake of all three sugars increased linearly in the range of sugar concentrations tested, which extended from 0.01 to 320 mm, denoting an insaturable system for sugar uptake. 14CO2 evolution was relatively low in all the experiments, the lowest evolution being recorded when the uptake of [14C]-sucrose was studied, while the highest 14CO2 evolution was recorded when the uptake of [14C]-glucose was studied. The data demonstrate a preferential utilisation of glucose over fructose and sucrose. In all the experiments, the two metabolic inhibitors significantly inhibited the decarboxylation of the three sugars.

Antomical Aspects of Citrus Abscission — Effects of Ethylene on Leaf and Fruit Explants

The anatomy of abscission has been attracting the attention of researchers in plant science for many years (2), and Hodgon’s pioneer work on the anatomy of leaf abscission (10) in citrus was published as early as 1918. In citrus we can define five abscission zones (AZs): the basal and laminar AZs of leaves, the shoot/peduncle (AZ-A) and calyx (AZ-C) AZs of fruit, and the AZ between style and ovary.