Accumulation of aquaporin mRNA in Sium latifolium under different water supply

BLIUMA D.A.

Institute of Botany of NASU

2, Tereschenkivska Str., Kyiv, 01601, Ukraine e-mail: dbluma@ukr.net

Water plays a fundamental role in the growth and development of plants. Plant growth and development depends on water. Supplying plants with water and nutrients occurs via the transport across cell membranes. This process can be disturbed by the influence of unfavourable environmental conditions.

Today it is known that transport of water through membranes is mediated by membrane proteins which form special water channels (D.-T. Luu, Maurel, 2005). At present the number of known aquaporins exceeds more then 200, moreover, considerable part of them are the plant aquaporins (Reizer et al, 1993).

Since water transport across plant cell membranes is done by specialized water channels, aquaporins, the regulation of aquaporins’ expression at the transcriptional and post-translational levels may be one of the mechanisms of regulation of the intracellular water balance during adaptation of plants to varying water supply.

The suitable object for studying water deficit effect on the expression of aquaporin genes is a water parsnip (Sium latifolium). This organism belongs to aerial-aquatic plants. It also capable to grow at terrestrial areas. This is an example of plant adaptation to changes in water supply. Since terrestrial forms of this plant are affected by the moderate water deficit comparing to aerial-aquatic ones we can study the expression patterns of aquaporin mRNA by comparing the terrestrial and aerial-aquatic ecotypes of Sium latifolium. Obtained results are very important for deeper understanding of mechanisms of plant adaptation to changes in their water supply.

This investigation has been carried out to determine whether water deficit alters aquaporin mRNA expression in terrestrial ecotype of Sium latifolium. The RT-PCR analysis of aquaporin mRNAs of the terrestrial and aerial-aquatic ecotypes of Sium latifolium demonstrated high differences between their expression patterns. The level of mRNA in the terrestrial ecotype of Sium latifolium was much higher compared to air-aquatic ecotype during vegetation, flowering and fruitage. We also analyzed actin 2 gene expression that was constant in both stressed and control ecotypes at all developmental stages.

According to different literature data water deficit has a strong impact on the expression of plant aquaporin genes(Guerrero et al, 1990; Fray et al, 1994; Yamada et al, 1997). Increased level of aquaporin transcripts in terrestrial form can be the evidence of high protein amount in cell membranes. Owing to it the water uptake under water deficit is enhanced and therefore the plant water balance is maintained at the normal level under unfavourable conditions.

REFERENCES

D.-T. Luu, Maurel C. Aquaporins in a challenging environment: molecular gears for adjusting plant water status // Plant Cell Envir. – 2005. – 28, N 1. – P. 85-96.

Fray R., Wallace A., Grierson D., Lycett G. Nucleotide sequence and expression of a ripening and water stress related cDNA from tomato with homology to the MIP class of membrane channel proteins // Plant Mol. Biol. – 1994. – 24, N 3. – P. 539-543.

Guerrero F., Jones J., Mullet J. Turgor responsive gene transcription and RNA levels increase rapidly when pea shoots are wilted. Sequence and expression of three inducible genes // Plant Mol. Biol. – 1990. – 15, N 1. – P. 11-26.

Reizer J., Reizer A., Saier M. The МІР family of integral membrane channel proteins: sequence comparisons, evolutionary relationships, reconstructed pathway of evolution, and proposed functional differentiation of the two repeated halves of the proteins // Crit. Rev. Biochem. Моl. Biol.

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Yamada S., Komori T., Myers P., Kuwata S., Kubo T., Imaseki H. Expression of plama membrane water channel genes under water stress in Nicotiana excelsior // Plant Cell Physiol. – 1997. – 38. – P. 1226-1231.

The effect of spectral structure

of light on physiological characteristics of microalgae

IEFIMOVA T.V., AKIMOV A.I.

Institute of Biology of the Southern Seas, Department of Ecological Physiology of Microalgae 2, Nakhimov Ave., Sevastopol, 99011, Crimea, Ukraine

e-mail: tatyana-iefimova@yandex.ru

The influence of various spectral structure of light on growth and photosynthetic characteristics of two species of microalgae (diatom Nitzschia sp. and cianobacterium Synechococcus elongatus) has been investigated. The intracellular content of carbon, Chl a and spectra of light absorption by pigments of alive algae and their acetone extracts have been determined.

Microalgae Nitzschia sp. and Synechococcus elongatys were adapted to limiting conditions of white, blue and red light (from 13 up to 40 mkEn) within two weeks. Incident light was calculated so that the quantity of the culture absorbed quanta were equal under all spectral cultivation conditions.

The growth rates of Nitzschia sp. and Synechococcus elongatys (division number per day) were similar at the white and red light adaptation, and growth rates were smaller at the blue light adaptation (30 % less for Nitzschia sp. and twice less for Synechococcus elongatys). The maximum quantum yield of photosynthesis (molecules О2 / quantum) was measured under conditions of white light. It was similar at the blue and white light adaptation. The maximum photosynthesis intensity (potential photosynthesis (mkg О2 / mkg Chl a h -1)) were also similar for blue and white light adaptation. Thus, though the algae grew more slowly under blue light, their potential photosynthetic activity remained high.

The С : Chl a relation was on average 30 for white light adaptation, 33 – for red light adaptation, 36 – for blue light adaptation of Nitzschia sp. at identical quantity of the absorbed quanta. The С : Chl a relation was on average 34 for white light adaptation, 27 – for red light adaptation, 44 – for blue light adaptation of Synechococcus elongatys. The considerable increase of the relation at algae adaptation at the blue light in comparison with the red light was due to the change of both values, i. e. the increase of carbon and the decrease of Chl a intracellular content. It should be mentioned, that C / Chl a relation correlates with the growth rate of algae in inverse dependence for both species of algae.

The shapes of light absorption spectra by alive cells of Nitzschia sp. did not change depending on conditions of cultivation. The increase of absorption on 620 nm (connected with the phycocyanin content increase) was observed for Synechococcus elongatys.

The shapes of light absorption spectra by pigments in 90 % acetone extract was practically identical, that proves that there is no appreciable influence of light quality on intracellular carotenoids to chlorophylls ratio.

Thus, the research made allows to draw a conclusion that the spectral structure of light doesn’t effect the photosynthetic characteristics of diatom Nitzschia sp. and cianobacterium Synechococcus elongatys. The observed decrease of algae growth rate at blue light is probably explained by significant absorption of this light by carotenoids, having lower efficiency of energy transfer to the reactionary centres of photosynthesis. «The complementary chromatic adaptation» of the considered species of algae has not been observed.

Історія ботанічної науки та етноботаніка / История ботанической науки и этноботаника / History of Plant Science and Ethnobotany