Murielle Eyletters

Quality assessment of urban trees: A comparative study of physiological characterisation, airborne imaging and on site fluorescence monitoring by the OJIP-test

The purpose of this paper is to demonstrate the complementary utility of chlorophyll fast fluorescence OJIP transient (from 50 microns to 1s) measurements in the aerial study of rows of trees. We identify limitations in photochemical events induced by urban injuries on Platanus acerfolia L. using the JIP-test procedure. The Performance Index (PIABS) showed the largest dynamic range to characterise the vitality of trees. Individual trees were graded into three quality groups based on the individual PIABS value compared to the overall average for trees in the alley. These groups are: high performers, with PIABS 50% higher than the alley average; normal trees, with a deviation from the alley average between -50% and %; and poor performers, whose deviation from the alley average was -50% or less. Trees also were grouped into five vitality categories on the basis of a stereoscopic and morphologic observation of the symmetry of tree crowns, percentage of defoliation and reflectance property in the visible and infra-red range. Here, we report a remarkable correlation between the airborne remote sensing data and the on-site fluorescence measurements.

Water stress induces overexpression of superoxide dismutases that contribute to the protection of cowpea plants against oxidative stress

Water stress is known to induce active oxygen species in plants. The accumulation of these harmful species must be prevented by plants as rapidly as possible to maintain growth and productivity. The aim of this study was to determine the effect of water stress on superoxide dismutase isozymes (SOD, EC 1.15.1.1.) in two cowpea cultivars [Vigna unguiculata L. Walp., cv. Bambey 21 (B21) and cv. TN88- 63]. Plants were submitted to water stress by withholding water supply and the expression of SOD was characterized during stress induction. In the same time, photosynthesis characteristics were determined through the measurement of the quantum yield of PS II photochemistry and the energy absorption rate per reaction centre. Results show how water stress regulates the synthesis and the activity of superoxide dismutase isoforms and how these enzymes contribute to protect photosynthesis against the damageable effects of superoxide radicals in cowpea. Increased MnSOD and FeSOD activity and concentration were shown to be induced by water stress and associated with protection of photosystem II photochemistry and whole plant growth against oxidative stress in these plants. On the contrary, plants unable to express high MnSOD and/or FeSOD isoforms showed more sensitivity to water stress.

Superoxide Dismutases Regulation in Cowpea (Vigna Unguiculata (L.) Walp.) Under Water Deficit Conditions

The most feared and the most widespread plant stress agents are active oxygen species. One regroups under the term « active oxygen species» all molecules derived of oxygen that possess a more or less great reactivity and aggressiveness towards membrane structures (lipids and proteins) and nuclear structures of plant or animal cell [1, 2]. Among these species are superoxide radicals (O2 -) and hydrogen peroxide (H2O2). Hydrogen peroxide is produced in peroxisomes during glycolate pathway and during enzymatic dismutation of superoxide radicals [1]. These reduced oxygen species are not only generated as by-products of endogenous biological reactions, but also their formation increases during biotic and non-biotic stress. Accumulation of superoxide radicals is prevented by superoxide dismutase (EC 1.15.1.1) which catalyses the dismutation of O2 - to O2 and H2O2 [3]. The three known types of this enzyme are distinguishable by their metal prosthetic part made of manganese (MnSOD), iron (FeSOD) or copper and zinc (Cu/ZnSOD), and by their behaviour towards specific inhibitors [2]. H2O2 is scavenged by catalases in the peroxisomes and by ascorbate peroxidase in Halliwell-Asada cycle [1, 4].