The Study On The Mechanisms Of Regulation For Stomatal Movements By Calcium Signals

Environmental factors can affect plant traits, whereas plants can also influence environmental condition through Stomatal regulation. The Stomatal transpiration and the CO₂ flux through stomata play essential roles in the global water and carbon cycle. Stomatal distribution, morphology and behavior respond to a spectrum of signals, from intracellular signaling to global climate changes. The studying Stomatal distribution or behavior can provide a link between microenvironment and ecological environment. Plants could adapt to environmental stresses through various signal transduction pathways. Studies on the signal transduction pathways may provide an insight into the interaction between plants and environments.We used several Arabidopsis mutants (cytokinin insensitive mutant, ethylene insensitive mutants, enhanced response to ABA mutant, AtPsiCaM over-expression/intervention transgenic plants, phosphate starvation response mutant) as materials to study some mechanisms of signal transduction in guard cells, as follows: (1) Stomatal index in these mutants were determined. (2) Further, we chose ethylene insensitive mutants (ein3-l and ein4) which showed much lower Stomatal index than the wild type as materials and measured their photosynthetic rate, transpiration rate, Stomatal conductance and intercellular CO2 partial pressure. Water use efficiency (WUE) and biomass were also determined. Then, we compared the properties of wrong-way Stomatal response (WWR) and the calcium signals among these Arabidopsis lines under the same conditions (3) Based on the logistic equation with a time-lag in population ecology, we constructed a calcium signal transporting message model with a time-lag to simulate the change of [Ca²⁺]_cyt in the cytoplasm system under different stimuli. Using a combination of theoretical and reported experimental work, we attempted to explore the mechanisms underlying Ca²⁺ oscillations in cytoplasm. (4) Furthermore, according to the relationship between the calcium signals and Stomatal response, we explored the quantitative relationship between the EF-hand motifs and the decoding of calcium signals. Here we hypothesized that the Ca²⁺ binding-induced conformational changes of EF-hand motifs took place one by one in CaMs or CaM-containing proteins, each happening at a specific rate and lasting for a specific calcium transient period. Based on this hypothesis, we developed a model of EF-hand motifs decoding calcium signals. We systematically varied calcium oscillation parameters in Arabidopsis guard cells, and then reanalyze the data from previous literatures.Several results and conclusions were obtained: (1) Results showed that these gene mutations imposed negative effects on Stomatal index. These responses might be regulated by calcium signal transduction pathway, cytokinin signal transduction pathway, ethylene signal transduction pathway, ABA signal transduction pathway and Pi signal transduction pathway. (2) Results showed that the functions of ein4 and ein3-1 genes were not limited to affecting Stomatal density and epidermal cell density, they also influenced WUE, biomass and calcium signals. The ein3-l and ein4 mutations might improve WUE and biomass by regulating cell development and mesophyll conductance, by affecting photosystem II (PSII) activaties, membrane fluidity and phospholipids through calcium signal transduction pathway. (3) Results showed that the intensity of initial stimuli and the sensitivity of calcium channels to stimuli not only influenced potential capacity of calcium concentration (P), but also influenced time-lag and intrinsic rate of increase per unit concentration (r). Lag time might determine the value of period of calcium signals, "P" might determine the amplitude, and "r" might determine the duration. (4) The results showed that the number of calcium transients with the best physiological effect was consistent with the predominant number of EF-hand motifs in CaM and CaM-containing proteins; a limited calcium oscillation period should be required for the activation of CaMs and CaM-containing proteins. With a limited range period, the calcium oscillations could induce the conformational change of EF-hand motifs. The present study was helpful to understand the mechanisms that decode Ca²⁺ signals in these proteins.In summary, we tried to study Stomatal distribution or behavior, which can provide a link between microenvironment and ecological environment. Our findings might be of great importance for a better understanding not only of plant response to environmental stress, but also of the encoding and decoding on calcium signals.