Heat‐Induced Leaf Senescence Associated with Chlorophyll Metabolism in Bentgrass Lines Differing in Heat Tolerance

Abstract

Leaf senescence is characterized by decreased chlorophyll content in leaves. The objectives of this study were to determine whether heat‐induced chlorophyll decline is due to inhibited chlorophyll synthesis or accelerated chlorophyll degradation and to determine whether genetic variations in heat tolerance of bentgrass (Agrostis spp.) species were associated with differential chlorophyll‐enzymatic responses to heat stress. Five turfgrass lines, including two transgenic creeping bentgrass (A. stolonifera L.) lines overexpressing isopentenyl transferase (ipt) gene ligated to a senescence‐activated promoter (SAG12) or heat shock promoter (HSP18.2) for controlling cytokinin synthesis, two thermal bentgrass (A. scabra Willd.) lines, and a wild‐type (WT) creeping bentgrass (‘Penncross’) were subjected to heat (38/33°C, day/night) or optimal temperature (22/18°C, day/night) (nonstress) for 42 d in growth chambers. The physiological parameters of turf quality, chlorophyll content, chlorophyll index, and dark green color index were measured. The data suggested significant genetic variations in the level of heat‐induced leaf senescence among the bentgrass lines. The enzyme activity of a key chlorophyll‐synthesizing enzyme, porphobilinogen deaminase, did not differ significantly across all the lines after 42 d of heat stress. The activities of chlorophyll‐degrading enzymes, including chlorophyllase and chlorophyll‐degrading peroxidase, increased significantly after heat stress, whereas pheophytinase activity was unchanged. Heat‐tolerant transgenic lines and thermal bentgrass maintained significantly lower activities of chlorophyll‐degrading enzymes than the WT under heat stress. Heat‐induced chlorophyll loss in bentgrass could be mainly due to accelerated chlorophyll degradation. Selecting for low chlorophyll degradation enzyme activity will help to facilitate the development of elite stay‐green bentgrass lines.

Sensitivity and Responses of Chloroplasts to Heat Stress in Plants

“…Under normal growth conditions, the synthesis and degradation of Chl reach equilibrium and the levels of this molecule remain stable (Ginsburg et al, 1994;Hörtensteiner, 2006;Wang et al, 2018). Conversely, when plants are subject to environmental stress, including heat, the content of Chl decreases, leading to leaf senescence or chlorosis Lim et al, 2007;Allakhverdiev et al, 2008;Rossi et al, 2017). Under heat treatment, the activity of chlorophyllase and Chl-degrading peroxidase dramatically increases, resulting in a serious reduction in Chl levels (Figure 2; Wang et al, 2018).…”

Metabolic Reprogramming in Chloroplasts under Heat Stress in Plants

“…In contrast, chlorophylls undergo turnover or breakdown when the partial or complete dismantling of the photosynthetic machinery occurs in response to environmental stresses, including heat stress. Heat stress symptoms in plants are typically characterized by leaf senescence or chlorosis due to a decline in chlorophyll content [ 2 , 51 , 52 ]. Heat-induced leaf chlorosis has been observed in a variety of plant species, including Arabidopsis [ 4 , 5 , 53 ], Soybean ( Glycine max L.…”

Beneficial role of acetylcholine in chlorophyll metabolism and photosynthetic gas exchange in Nicotiana benthamiana seedlings under salinity stress

“…It has been reported that regulation of chlorophyll biosynthesis in plants depends on the intensity and type of stress, such as water stress (Dalal & Tripathy ), salt stress (Turan & Tripathy ) and heat stress (Rossi et al . ). Protoporphyrin IX (Proto IX) is one of the end products of the chlorophyll biosynthetic pathway.…”