Changes in Carbohydrate Metabolism in Coconut Palms Infected with the Lethal Yellowing Phytoplasma

Abstract

Lethal yellowing (LY), a disease caused by a phytoplasma, is the most devastating disease affecting coconut (Cocos nucifera) in Mexico. Thousands of coconut palm trees have died on the Yucatan peninsula while plantations in Central America and on the Pacific coast of Mexico are severely threatened. Polymerase chain reaction assays enable identification of incubating palm trees (stage 0+, phytoplasma detected but palm asymptomatic). With the development of LY, palm trees exhibit various visual symptoms such as premature nut fall (stage 1), inflorescence necrosis (stages 2 to 3), leaf chlorosis and senescence (stages 4 to 6), and finally palm death. However, physiological changes occur in the leaves and roots prior to onset of visual symptoms. Stomatal conductance, photosynthesis, and root respiration decreased in stages 0+ to 6. The number of active photosystem II (PSII) reaction centers decreased during stage 2, but maximum quantum use efficiency of PSII remained similar until stage 3 before declining. Sugar and starch concentrations in intermediate leaves (leaf 14) and upper leaves (leaf 4) increased from stage 0- (healthy) to stages 2 to 4, while root carbohydrate concentrations decreased rapidly from stage 0- to stage 0+ (incubating phytoplasma). Although photosynthetic rates and root carbohydrate concentrations decreased, leaf carbohydrate concentrations increased, suggesting inhibition of sugar transport in the phloem leading to stress in sink tissues and development of visual symptoms of LY.

Relationships between leaf pigments and photosynthesis in common bean plants infected by anthracnose

“…Our results suggest that susceptible plants present slow stomatal closing during the infection process (significant reduction was found only on the 12th day after inoculation). Similar results on stomatal conductance reduction caused by infection of Colletotrichum lindemuthianum in Phaseolus vulgaris leaves were reported by Meyer et al (2001) and by Maust et al (2003) in Cocos nucifera plants.…”

cDNA-AFLP analysis of gene expression changes in apple trees induced by phytoplasma infection during compatible interaction

“…3). Deregulation of the key genes in photosynthesis could participate to AP symptom expression as already reported (Jagoueix-Eveillard et al 2001;Maust et al 2003;Bertamini et al 2004). 2) The second group encloses genes involved in the symptom expression (Fig.…”

“…3). 1) Two genes related to photosystems I and II (PSI & PSII) that were down-regulated only in the symptomatic part of plants were identified, and underexpression of these genes is probably due to carbohydrate accumulation in symptomatic leaves (Maust et al 2003). Moreover, the expression of a gene coding for fructose-1,6-bisphosphatase (FBPase) was reduced in the infected plants.…”

Changes in photosynthetic pigment and carbohydrate content in common bean cultivars infected by Colletotrichum lindemuthianum

“…Results obtained by Lopes and Berger (2001) working with P. vulgaris, as well as Leon et al (1996) and Scarpari et al (2005) revealed changes in photosynthetic pigments after pathogen infection in susceptible plants. The accumulation of carbohydrates under conditions of biotic and abiotic stress are described by Maust et al (2003) and Lobato et al (2008a). The aim of this study was to investigate the changes in photosynthetic pigment and carbohydrate contents in the cultivars Mexico 222 (resistant) and Widusa (susceptible) infected by race 23 of Colletotrichum lindemuthianum.…”