Salt Tolerance in Crop Plants Monitored by Chlorophyll Fluorescence In Vivo

Abstract

The potential of measurements of chlorophyll fluorescence in vivo to detect cellular responses to salinity and degrees of salt stress in leaves was investigated for three crop plants. Sugar beet (Beta vulgaris L.) (salt tolerant), sunflower (Heliandtws annuus L.) (moderately salt tolerant), and bean (Phaseohis Vulgaris L. cv Canadian Wonder) (salt intolerant) were grown in pots and watered with mineral nutrient solution containing 100 millimolar NaCI. The fast rise in variable chlorophyll fluorescence yield that is correlated with photoreduction of photosystem II acceptors increased in leaves of sugar beet plants treated with salt suggesting stimulation of photosystem II activity relative to photosystem I. In sunflower, this fast rise was depressed by approximately 25% and the subsequent slow rate of quenching of the chlorophyll fluorescence was stimulated. These differences were more marked in the older mature leaves indicating an increasing gradient of salt response down the plant. The salt effect in vivo was reversible since chloroplasts isolated from mature leaves of salt-treated and control sunflower plants gave similar photosystem II activities. Unlike in sugar beet and sunflower, leaves of salt-treated bean progressively lost chlorophyll. The rate of slow quenching of chlorophyll fluorescence decreased indicating development of a partial block after photosystem II and possible initial stimulation of photosystem II activity. With further loss of chlorophyll photosystem II activity declined. It was concluded that measurements of chlorophyll fluorescence in vivo can provide a rapid means of detecting salt stress in leaves, including instances where photosynthesis is reduced in the absence of visible symptoms. The possible application to screening for salt tolerance is discussed.Increasing salinity in soil and water and its effect on crop plants has become a vast problem for agriculture in arid and semiarid regions that depend on irrigation. It has been estimated that agriculture in one-third of the land irrigated worldwide is already plagued by excess salinity (9). Further, problems of salinity are not confined to irrigated fields, but now extend to large areas of nonirrigated farmlands across the plains of North American and southern Australia. Although much effort is being expended in water control schemes and engineering projects to improve saline environments, as pointed out by Epstein et al. (9), these serve to minimize the problem of salinity but cannot eliminate it and the need to develop salt-tolerant crops at the same time has been emphasized (9, 21).Visible symptoms, frequently leaf burns, are rather late manifestations of severe salt stress, and except in a few instances, e.g. citrus (19), the salt content of leaves or roots is not a reliable guide to salt tolerance. New methods are required to monitor salt stress in physiological studies, to detect adverse effects of salt on fieldgrown crops that reduce yield without producing visible symptoms, and in the selection of salt-tolerant strain...

Photosynthesis and Ion Content of Leaves and Isolated Chloroplasts of Salt-Stressed Spinach

“…The electron transport rate for intact chloroplasts or thylakoids was only slightly less than the control chloroplasts, in agreement with previous results for sunflower (22). Baker (2) found that high concentrations of NaCl or KCI inhibited electron transport when added to isolated spinach thylakoids.…”

Characterization of PSII photochemistry in salt‐adapted cells of cyanobacterium Spirulina platensis

“…Some studies have shown that, in higher plants, salt stress inhibits PSII activity (Bongi & Loreto, 1989 ;Mishra et al, 1991 ;Masojidek & Hall, 1992 ;Belkhodja et al, 1994 ;Everard et al, 1994), whereas others have indicated that salt stress has no effect on PSII (Robinson et al, 1983 ;Brugnoli & Bjo$ rkman, 1992 ;Morales et al, 1992) or even increases PSII activity (Smillie & Nott, 1982). In cyanobacteria, the effect of salt stress of PSII has not been studied as intensively as in higher plants.…”

Variações sazonais de aspectos fisiológicos de espécies da Caatinga

“…A medição da fluorescência da clorofila pode ser usada para revelar informações sobre os estádios de desenvolvimento de plantas (Bacarin & Mosquin 2002), para comparar genótipos (Portes & Magalhães, 1993;Campostrini & Maestri, 1998) e é usada, também, para investigar danos causados no aparato fotossintético, por diversas causas de estresses (Smille & Not, 1982;Strant & Oquist, 1988;Havaux et al, 1988;Torres Neto et al, 2002;El-Sheekh, 1993). Esta variável é uma significativa informação da eficiência fotoquímica do processo fotossintético (Torres Neto et al, 2002) Desta forma, as aferições da fluorescência e do potencial hídrico de espécies da Caatinga, que constituem objetivos deste trabalho, podem contribuir para o entendimento do processo evolutivo dessas plantas sob condições adversas, permitindo caracterizar as diferenças fisiológicas nas duas estações características da Região Nordeste, o período chuvoso e o período de estiagem.…”