Photo-oxidative stress in coconut seedlings: early events to leaf scorching and seedling death

Abstract

Experiments were conducted on coconut seedlings to delineate events of photo-oxidative stress damage. Studies on chlorophyll fluorescence indicated a clear case of excess light energy under high light conditions causing stress to coconut seedlings raised under coconut palms. Quantum yield of photo-chemistry of leaflets exposed to high light was significantly less than those under shade. Seedlings exposed to high light and then shifted to shade have shown significant improvement in quantum yield. Excess light energy harvested by chlorophyll antenna caused high non-photochemical quenching resulting in production of biologically toxic super oxide, hydrogen peroxide and hydroxyl radicals. It is apparent that photoinhibition of photosynthesis takes place due to i) PSII down regulation and ii) damage to PS II system in initial stages of exposure to excess light and under prolonged exposures inhibition is caused due to iii) chlorophyll bleaching and iv) damage to chloroplast and cell membrane integrity, followed by reduction in photosynthetically active leaf area because of scorching thus reducing canopy photosynthesis. Protein concentration in leaf tissue was higher in seedlings in high light conditions. Three distinct low molecular weight proteins with pI of 4.9, 8.4 and 10.15 having M r less than 20,000 were found in seedlings exposed to high light intensities. Results clearly demonstrate the events that take place at early stage to subsequent cascading effects leading to the scorching and death of leaf and even seedling death under severe conditions.

Micropropagation of Guadua chacoensis (Rojas) Londoño & P. M. Peterson1

“…An initial decrease is commonly reported during the first days after the ex vitro transfer (Yang & Yeh 2008) and occurred more rapidly in no shading and low shading than in high shading treatments. A significant increase in the photon flux density leads to photoinhibition, and a long-term disparity in the quantum yield may lead to a photosynthesis down regulation by photodamage (Naresh & Bai 2009). The no shading and low shading treatments resulted in leaves with basipetal chlorophyll bleaching followed by foliar abscission on most of the tracked leaves (100 % and 90 %, respectively) on the 12nd day, thus suggesting symptoms of a photo-oxidative stress caused by the evolution of the reactive oxidative species due to an excess of light.…”

Different photoprotective strategies for white leaves between two co‐occurring Actinidia species

“…For A. kolomikta and A. polygama , variegated leaves appear in white color from the adaxial surface and in green color from the abaxial surface at the mature stage. Hence, white leaves of A. kolomikta and A. polygama are neither the result of photobleaching (Užarević et al, 2011) nor of mutations (e.g., Var variegation and reticulate mutants) (Aluru et al, 2006; Liu et al, 2010; Lundquist et al, 2014; Naresh & Kasturi Bai, 2009). White leaves of A. kolomikta and A. polygama are white since their emergence, but they can grow as normally as green leaves.…”

Lower photosynthetic capacity under higher spectral reflectance? The case of Actinidia polygama

“…In A. polygama, variegated leaves are white on the adaxial surface, but the entire abaxial surface is green. Hence, white leaves of A. polygama are different from photobleaching and white mutants (for example Varvariegation and reticulate mutants), which are mainly due to damage caused by reactive oxygen species (Takahashi et al 2002, Naresh and Bai 2009, Uzarevic et al 2011 and completely defective chloroplast development (Aluru et al 2006, Liu et al 2010, Lundquist et al 2014. These latter kinds of mutation usually belong to lethal genotypes, and the lifespan of such leaves is very short.…”