This study investigated whether gas exchange and the present content of antioxidant compounds can contribute to the survival of Euterpe oleracea plants in environments of frequent waterlogging. A factorial randomised, experimental design included two distinct water conditions (waterlogging and control) and five evaluation times (0, 6, 12, 18, and 24 d). Gasexchange parameters, leaf temperature, electrolyte leakage, and contents of antioxidant compounds were measured. Waterlogging did not promote significant alterations in net photosynthetic rate and transpiration, and stomatal conductance was reduced only after 18 d. Malondialdehyde and glutathione contents did not significantly change during waterlogging. Additionally, electrolyte leakage was significant only after 18 d of waterlogging. Thus, this study revealed that maintenance in gas exchange and antioxidant compounds might contribute to the survival of E. oleracea plants in environments exposed to waterlogging.

Euterpe oleracea (Mart.), an Amazonian palm, is of economic importance due to the production of energy drinks. Plants exposed to waterlogging are prone to damage at the cellular level and cause irreversible metabolic dysfunctions leading to cell death. This study was aimed to study cell damages and to investigate enzyme activities related to antioxidant system in this specie. The experimental design was in factorial randomized with two water conditions (waterlogging and control) and five evaluation times (0, 6, 12, 18, and 24 days). The parameters measured were electrolyte leakage (EL), contents of hydrogen peroxide (H 2 O 2 ), malondialdehyde (MDA) and glutathione (GSH), and enzymatic activities of catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POX) in leaf and root tissues. Waterlogging did not promote significant modifications in EL, MDA and H 2 O 2 in both the tissues evaluated, and a minor alteration in GSH was observed only in the roots. Significant increases in the activity of CAT, APX and POX were observed in leaf and roots, at early stages. It can thus be concluded that CAT, APX and POX were efficient in controlling EL and MDA in leaf and root of E. oleracea plants under waterlogging.

Small cylinders of red beet (Beta vulgaris) root were frozen at various rates. Ultraslow cooling at 0.2 C per hour to -4 C produced little damage, as determined by leakage of pigment and electrolytes, and softening. All of these increased at faster rates of cooling or at lower temperatures. Cooling at the ultraslow rate appears to induce extracellular freezing, resulting in a protective dehydration of the cell contents.with the requirements of large pieces of tissue, encourage the formation of extracellular ice with consequent partial dehydration of the protoplast. These are conditions that can preserve the frozen cell (10), and appear also to contribute to the natural process of freeze-hardening (7,8

MATERIALS AND METHODSCylinders measuring 5 mm in diameter were punched from fresh fruits or vegetables with a cork borer, trimmed to a length of 20 mm, and used without washing. Temperature at the center was measured with a thermistor mounted in a 24-gauge hypodermic needle and recorded as described previously (4). Tissues studied included primarily the parenchyma of cucumber (Cucumis sativus), peach (Prunus persica) and cantaloupe (Cucumis melo cantalupensis). Other tissues studied are listed in Table I. Specimens were frozen by immersion in octafluorocyclobutane (Freon C-318,' b.p. -5.8 C).In order to observe the effect of degree of sample hydration upon the shape of the freezing curve, weighed cylinders cut longitudinally from cucumber fruits were held for 3 hr at constant relative humidity over saturated salt solutions (NaCl, 76% RH5; Mg(NO4),, 54% RH; KCO,CH,, 25% RH) or over distilled water at room temperature. In some experiments, this treatment was followed by rehydration in water for 2 hr prior to freezing.Tests for determining degree of cell rupture by loss of pigments or electrolytes, and degrees of softening by increased compressibility were described previously (3). RESULTSTypical freezing curves for cylindrical sections of cucumber are shown in Figure 1. Initiation of freezing was followed by the first freezing region (FR-1) or plateau. After a temperature drop, there was usually a second freezing region (FR-2) of reduced slope, although not necessarily a plateau, with a great number of temperature spikes and a shape characteristic of the tissue. The variability in intensity of these spikes in freezing curves of a number of other edible tissues is presented in Table I. Figure 2 shows some of the variations possible in these freezing curves (Fig. 2A)