Heat Reduces Nitric Oxide Production Required for Auxin-Mediated Gene Expression and Fate Determination in Tree Tobacco Guard Cell Protoplasts

Abstract

Tree tobacco (Nicotiana glauca) is an equatorial perennial with a high basal thermotolerance. Cultured tree tobacco guard cell protoplasts (GCPs) are useful for studying the effects of heat stress on fate-determining hormonal signaling. At lower temperatures (32°C or less), exogenous auxin (1-naphthalene acetic acid) and cytokinin (6-benzylaminopurine) cause GCPs to expand 20-to 30-fold, regenerate cell walls, dedifferentiate, reenter the cell cycle, and divide. At higher temperatures (34°C or greater), GCPs expand only 5-to 6-fold; they do not regenerate walls, dedifferentiate, reenter the cell cycle, or divide. Heat (38°C) suppresses activation of the BA auxin-responsive transgene promoter in tree tobacco GCPs, suggesting that inhibition of cell expansion and cell cycle reentry at high temperatures is due to suppressed auxin signaling. Nitric oxide (NO) has been implicated in auxin signaling in other plant systems. Here, we show that heat inhibits NO accumulation by GCPs and that L-N G -monomethyl arginine, an inhibitor of NO production in animals and plants, mimics the effects of heat by limiting cell expansion and preventing cell wall regeneration; inhibiting cell cycle reentry, dedifferentiation, and cell division; and suppressing activation of the BA auxin-responsive promoter. We also show that heat and L-N G -monomethyl arginine reduce the mitotic indices of primary root meristems and inhibit lateral root elongation similarly. These data link reduced NO levels to suppressed auxin signaling in heat-stressed cells and seedlings of thermotolerant plants and suggest that even plants that have evolved to withstand sustained high temperatures may still be negatively impacted by heat stress.The three major interrelated abiotic plant stresses accompanying global climate change are increasing concentrations of atmospheric CO 2 , heat, and drought (Mittler,

Nitric Oxide (NO) in Plant Heat Stress Tolerance: Current Knowledge and Perspectives

“…Furthermore, the reduced NO levels in C. morifolium seedlings was followed by a sequence of events such as reduced S- nitrasoglutathione reductase (GSNOR) activity, accumulation of SNOs, an increase in peroxynitrites and consequently intensified protein tyrosine nitration (Chaki et al, 2011 ). Similarly, heat stress at 38°C for 16 h reduced NO accumulation in the guard cell protoplasts of tree Nicotiana glauca (Beard et al, 2012 ). Abolishing internal NO levels by the treatment with a well- known NO synthase (NOS) inhibitor, L-N(G)-nitroarginine methyl ester, also resulted in similar effects of heat stress in these cells.…”

“…Exogenous application of NO donors has also been able to reduce heat-induced cellular damage further underlining the involvement of NO in plant heat response (Song et al, 2006 ; Hasanuzzaman et al, 2013 ). Diverse cellular sites of NO synthesis have been documented previously under heat stress, mostly based on the fluorescent dyes such as 5,6- diaminofluorescein diacetate (Beard et al, 2012 ). For instance, heat stress induced NO-fluorescence was observed in diverse cell types in N. tabacum , including palisade mesophyll cells, all epidermal cell types, such as guard cells, subsidiary cells, long and short trichomes.…”

Electrochemical Sensors for Nitric Oxide Detection in Biological Applications

“…Protection methods to achieve high selectivity by preventing the interference of charged species (including anionic ascorbic acid, uric acid, neutral acetaminophen and cationic dopamine) were summarized. NO electrochemical sensors for detecting NO level in single cell 17, multi‐cell 21, kidney 22, 23, brain 24–26, heart 27, liver 28, 29, human blood serum samples 30, and plant cells 31–33 were detailed. The trends for developing a novel NO sensor were outlooked in the last part.…”

Reactive Nitrogen Species and the Role of NO in Abiotic Stress

“…Hasanuzzaman et al (2013) suggested that ABA may impart thermotolerance by raising the level of NO. On the contrary, heat inhibited NO accumulation in cultured guard cell protoplasts of Nicotiana glauca (tree tobacco) (Beard et al, 2012). Most probably the observed effects were related to the antioxidant action of NO, which elevates negative effects caused by the intensification of peroxidative metabolism under thermal stress .…”