Supra-optimal root-zone temperatures, growth and stomatal conductance

The influence of supra-optimal root-zone temperatures on growth and stomatal conductance in Capsicum annuum L.

by Dodd I. C., He J.,Turnbull C. G. N., Lee S. K., Critchley C. (2000)

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In Journal of Experimental Botany 51(343,): 239–248 – https://doi.org/10.1093/jexbot/51.343.239 –

https://academic.oup.com/jxb/article/51/343/239/481172

Abstract

Pepper (Capsicum annuum L.) plants were grown aeroponically in a Singapore greenhouse under natural diurnally fluctuating ambient shoot temperatures, but at two different root-zone temperatures (RZTs): a constant 20±2 °C RZT and a diurnally fluctuating ambient (A) ( 25–40 °C) RZT. Plants grown at 20-RZT had more leaves, greater leaf area and dry weight than A-RZT plants. Reciprocal transfer experiments were conducted between RZTs to investigate the effect on plant growth, stomatal conductance (g_s) and water relations. Transfer of plants from A-RZT to 20-RZT increased plant dry weight, leaf area, number of leaves, shoot water potential (𝚿_shoot), and g_s; while transfer of plants from 20-RZT to A-RZT decreased these parameters. Root hydraulic conductivity was measured in the latter transfer and decreased by 80% after 23 d at A-RZT. Transfer of plants from 20-RZT to A-RZT had no effect on xylem ABA concentration or xylem nitrate concentration, but reduced xylem sap pH by 0.2 units. At both RZTs, g_s measured in the youngest fully expanded leaves increased with plant development. In plants with the same number of leaves, A-RZT plants had a higher g_s than 20-RZT plants, but only under high atmospheric vapour pressure deficit. The roles of chemical signals and hydraulic factors in controlling g_s of aeroponically grown Capsicum plants at different RZTs are discussed.

Do increases in xylem sap pH and/or ABA concentration mediate stomatal closure following nitrate deprivation?

by Dodd I. C., Tan L. P., He J. (2003)

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In Journal of Experimental Botany 54: 1281-1288 – https://doi.org/10.1093/jxb/erg122 –

https://academic.oup.com/jxb/article/54/385/1281/592753

Abstract

Stomatal conductance (g_s) of pepper (Capsicum annuum L.) plants decreased during the second photoperiod (day 2) after withholding nitrate (N). Stomatal closure of N‐deprived plants was not associated with a decreased shoot water potential (Ψ_shoot); conversely Ψ_shoot was lower in N‐supplied plants. N deprivation transiently (days 2 and 3) alkalized (0.2–0.3 pH units) xylem sap exuded from de‐topped root systems under root pressure, and xylem sap expressed from excised shoots by pressurization. The ABA concentration of expressed sap increased 3–4‐fold when measured on days 2 and 4. On day 2, leaves detached from N‐deprived and N‐supplied plants showed decreased transpiration rates when fed an alkaline (pH 7) artificial xylem (AX) solution, independent of the ABA concentration (10–100 nM) supplied. Thus changes in xylem sap composition following N deprivation can potentially close stomata. However, the lower transpiration rate of detached N‐deprived leaves relative to N‐supplied leaves shows that factors residing within N‐deprived leaves also mediate stomatal closure, and that these factors assume greater importance as the duration of N deprivation increases.

Ethylene and stomatal closure

 

Ethylene mediates UV-B-induced stomatal closure via peroxidase-dependent hydrogen peroxide synthesis in Vicia faba L.

by He J., Yue X., Wang R., Zhang Y. (2011)

in J. Exp. Bot. 62, 2657–2666. doi: 10.1093/jxb/erq431 –

PubMed Abstract | CrossRef Full Text | Google Scholar 

http://jxb.oxfordjournals.org/content/62/8/2657

Abstract

Ultraviolet B (UV-B) radiation is an important environmental signal for plant growth and development, but its signal transduction mechanism is unclear. UV-B is known to induce stomatal closure via hydrogen peroxide (H₂O₂), and to affect ethylene biosynthesis.

As ethylene is also known to induce stomatal closure via H₂O₂ generation, the possibility of UV-B-induced stomatal closure via ethylene-mediated H₂O₂ generation was investigated in Vicia faba by epidermal strip bioassay, laser-scanning confocal microscopy, and assays of ethylene production.

It was found that H₂O₂ production in guard cells and subsequent stomatal closure induced by UV-B radiation were inhibited by interfering with ethylene biosynthesis as well as ethylene signalling, suggesting that ethylene is epistatic to UV-B radiation in stomatal movement.

Ethylene production preceded H₂O₂production upon UV-B radiation, while exogenous ethylene induced H₂O₂production in guard cells and subsequent stomatal closure, further supporting the conclusion. Inhibitors for peroxidase but not for NADPH oxidase abolished H₂O₂ production upon UV-B radiation in guard cells, suggesting that peroxidase is the source of UV-B-induced H₂O₂production.

Taken together, our results strongly support the idea that ethylene mediates UV-B-induced stomatal closure via peroxidase-dependent H₂O₂ generation.

The relationship between NO and H2O2 during UV-B-regulated stomatal movement.

 

The role and the interrelationship of hydrogen peroxide and nitric oxide in the UV-B-induced stomatal closure in broad bean

by He J., Xu H., She X.-P., Song X.-G., Zhao W.-M. (2005)

in Funct. Plant Biol. 32, 237–247. doi: 10.1071/FP04185 –

CrossRef Full Text | Google Scholar

http://www.publish.csiro.au/?paper=FP04185

Abstract

Previous studies have showed that UV-B can stimulate closure as well as opening of stomata. However, the mechanism of this complex effect of UV-B is not clear.

The purpose of this paper is to investigate the role and the interrelationship of H₂O₂ and NO in UV-B-induced stomatal closure in broad bean (Vicia fabaL.).

By epidermal strip bioassay and laser-scanning confocal microscopy, we observed that UV-B-induced stomatal closure could be largely prevented not only by NO scavenger c-PTIO or NO synthase (NOS) inhibitor l-NAME, but also by ascorbic acid (ASC, an important reducing substrate for H₂O₂ removal) or catalase (CAT, the H₂O₂ scavenger), and that UV-B-induced NO and H₂O₂ production in guard cells preceded UV-B-induced stomatal closure.

These results indicate that UV-B radiation induces stomatal closure by promoting NO and H₂O₂ production. In addition, c-PTIO, l-NAME, ASC and CAT treatments could effectively inhibit not only UV-B-induced NO production, but also UV-B-induced H₂O₂ production. Exogenous H₂O₂-induced NO production and stomatal closure were partly abolished by c-PTIO and l-NAME.

Similarly, exogenous NO donor sodium nitroprusside-induced H₂O₂ production and stomatal closure were also partly reversed by ASC and CAT.

These results show a causal and interdependent relationship between NO and H₂O₂ during UV-B-regulated stomatal movement. Furthermore, the l-NAME data also indicate that the NO in guard cells of Vicia faba is probably produced by a NOS-like enzyme.