Andrzej Bajguz

Effects of brassinosteroids on the plant responses to environmental stresses.

Brassinosteroids are found in a wide range of organisms from lower to higher plants. They are steroidal plant hormones implicated in the promotion of plant growth and development. Brassinosteroid metabolism has long been known to be altered in plants responding to abiotic stresses and to undergo profound changes in plants interacting with bacterial, fungal and viral pathogens. This review describes the role of brassinosteroids in response to various kinds of stresses via activation of different mechanisms.

The chemical characteristic and distribution of brassinosteroids in plants.

Brassinosteroids represent a class of plant hormones with high-growth promoting activity. They are found at low levels in pollen, anthers, seeds, leaves, stems, roots, flowers, grain, and young vegetative tissues throughout the plant kingdom. Brassinosteroids are a family of about 60 phytosteroids. The article gives a comprehensive survey on the hitherto known brassinosteroids isolated from plants. The chemical characteristic of brassinosteroids is also presented.

Conjugates of auxin and cytokinin.

Plant growth and developmental processes as well as environmental responses require the action and cross talk of phytohormones including auxins and cytokinins. Active phytohormones are changed into multiple forms by acylation, esterification or glycosylation, for example. It seems that conjugated compounds could serve as pool of inactive phytohormones that can be converted to active forms by de-conjugation reactions. The concept of reversible conjugation of auxins and cytokinins suggests that under changeable environmental, developmental or physiological conditions these compounds can be a source of free hormones. Phytohormones metabolism may result in a loss of activity and decrease the size of the bioactive pool. All metabolic steps are in principle irreversible, except for some processes such as the formation of ester, glucoside and amide conjugates, where the free compound can be liberated by enzymatic hydrolysis. The role, chemistry, synthesis and hydrolysis of conjugated forms of two classes of plant hormones are discussed.

Brassinosteroid enhanced the level of abscisic acid in Chlorella vulgaris subjected to short-term heat stress.

The present study was undertaken to test the influence of exogenously applied 10nM brassinolide (BL) on the abscisic acid (ABA) content in Chlorella vulgaris cultures subjected to short-term (3h) heat stress (30-40 degrees C). We found that BL enhanced the ABA content with increase in temperature. In parallel, under these conditions treatment with BL resulted in growth levels very similar to those of control cell cultures (non-treated). BL had no significant effect on the content of chlorophyll or sugar in Chlorella vulgaris cells. Only a slight effect of BL on the protein content was observed. Under normal growth conditions (25 degrees C), BL showed a minor increase in the ABA content in Chlorella vulgaris cells. The present work also demonstrates that Chlorella vulgaris can synthesize ABA. This is the first evidence of ABA detection in Chlorella vulgaris cells.

Conjugates of abscisic acid, brassinosteroids, ethylene, gibberellins, and jasmonates

Phytohormones, including auxins, abscisic acid, brassinosteroids, cytokinins, ethylene, gibberellins, and jasmonates, are involved in all aspects of plant growth, and developmental processes as well as environmental responses. However, our understanding of hormonal homeostasis is far from complete. Phytohormone conjugation is considered as a part of the mechanism to control cellular levels of these compounds. Active phytohormones are changed into multiple forms by acylation, esterification or glycosylation, for example. It seems that conjugated compounds could serve as pool of inactive phytohormones that can be converted to active forms by de-conjugation reactions. Some conjugates are thought to be temporary storage forms, from which free active hormones can be released after hydrolysis. It is also believed that conjugation serves functions, such as irreversible inactivation, transport, compartmentalization, and protection against degradation. The nature of abscisic acid, brassinosteroid, ethylene, gibberellin, and jasmonate conjugates is discussed.

Synergistic effect of auxins and brassinosteroids on the growth and regulation of metabolite content in the green alga Chlorella vulgaris (Trebouxiophyceae).

The relationships between brassinosteroids (BRs) (brassinolide, BL; 24-epiBL; 28-homoBL; castasterone, CS; 24-epiCS; 28-homoCS) and auxins (indole-3-acetic acid, IAA; indole-3-butyric acid, IBA; indole-3-propionic acid, IPA) in the regulation of cell number, phytohormone level and metabolism in green alga Chlorella vulgaris were investigated. Exogenously applied auxins had the highest biological activity in algal cells at 50 μM. Among the auxins, IAA was characterized by the highest activity, while IBA - by the lowest. BRs at 0.01 μM were characterized by the highest biological activity in relation to auxin-treated and untreated cultures of C. vulgaris. The application of 50 μM IAA stimulated the level of all detected endogenous BRs in C. vulgaris cells. The stimulatory effect of BRs in green algae was arranged in the following order: BL > 24-epiBL > 28-homoBL > CS > 24-epiCS > 28-homoCS. Auxins cooperated synergistically with BRs stimulating algal cell proliferation and endogenous accumulation of proteins, chlorophylls and monosaccharides in C. vulgaris. The highest stimulation of algal growth and the contents of analyzed biochemical parameters were observed for the mixture of BL with IAA, whereas the lowest in the culture treated with both 28-homoCS and IBA. However, regardless of the applied mixture of BRs with auxins, the considerable increase in cell number and the metabolite accumulation was found above the level obtained in cultures treated with any single phytohormone. Obtained results confirm that both groups of plant hormones cooperate synergistically in the control of growth and metabolism of unicellular green alga C. vulgaris.

The Use of Algae Chlorella vulgaris Immobilized on Cellex‐T Support for Separation/Preconcentration of Trace Amounts of Platinum and Palladium before GFAAS Determination

Abstract The ability of green algae Chlorella vulgaris, immobilized on Cellex‐T support, for selective binding of platinum (Pt) and palladium (Pd) from acidic solutions (at pH range 1.5–1.8) has been demonstrated. The use of immobilized algae packed into a microcolumn (150 mg) in a flow mode provides good efficiency and reproducibility of the biosorption process (95.2 ± 0.4% for Pt and 99.3 ± 0.9% for Pd). The presence of seven interfering ions up to their 100 µg mL−1 concentration does not influence Pt and Pd retention on the column. The best efficiency of elution for both metals from the column was obtained with 0.3 mol L−1 thiourea (TU) in 1 mol L−1 hydrochloric acid used as a stripping reagent The detection limits obtained by the optimized method, followed by graphite furnace atomic absorption spectrometric detection for Pt and Pd, were 0.2 and 0.096 ng mL−1, respectively. The proposed method was applied for matrix separation and determination of Pt and Pd by graphite furnace atomic absorption spectrometry (GFAAS) in spiked tap water, wastewater, and grass samples.

Interactive effect of brassinosteroids and cytokinins on growth, chlorophyll, monosaccharide and protein content in the green alga Chlorella vulgaris (Trebouxiophyceae)

Interaction between brassinosteroids (BRs) (brassinolide, BL; 24-epibrassinolide, 24-epiBL; 28-homobrassinolide, 28-homoBL; castasterone, CS; 24-epicastasterone, 24-epiCS; 28-homocastasterone, 28-homoCS) and adenine- (trans-zeatin, tZ; kinetin, Kin) as well as phenylurea-type (1,3-diphenylurea, DPU) cytokinins (CKs) in the regulation of cell number, phytohormone level and the content of chlorophyll, monosaccharide and protein in unicellular green alga Chlorella vulgaris (Trebouxiophyceae) were examined. Chlorella vulgaris exhibited sensitivity to CKs in the following order of their stimulating properties: 10 nM tZ > 100 nM Kin >1 μM DPU. Exogenously applied BRs possessed the highest biological activity in algal cells at concentration of 10 nM. Among the BRs, BL was characterized by the highest activity, while 28-homoCS - by the lowest. The considerable increase in the level of all endogenous BRs by 27-46% was observed in C. vulgaris culture treated with exogenous 10 nM tZ. It can be speculated that CKs may stimulate BR activity in C. vulgaris by inducing the accumulation of endogenous BRs. CKs interacted synergistically with BRs increasing the number of cells and endogenous accumulation of proteins, chlorophylls and monosaccharides in C. vulgaris. The highest stimulation of algal growth and the contents of analyzed biochemical parameters were observed for BL applied in combination with tZ, whereas the lowest in the culture treated with both 28-homoCS and DPU. However, regardless of the applied mixture of BRs with CKs, the considerable increase in cell number and the metabolite accumulation was found above the level obtained in cultures treated with any single phytohormone in unicellular green alga C. vulgaris.

Brassinosteroids and lead as stimulators of phytochelatins synthesis in Chlorella vulgaris

Summary The effect of brassinosteroids 10 −8 mol/L (BR) (brassinolide, BL; 24-epiBL; homoBL; castasterone, CS; 24-epiCS; homoCS) together with two levels of lead (10 −6 and 10 −4 mol/L) on the phytochelatins (PC) content of Chlorella vulgaris was studied. The BR and lead (10 −4 mol/L) showed a stronger stimulation of the synthesis of PC by the algal cell than the culture treated with lead alone. The effect of BR and lead on Chlorella vulgaris growth was very quick. The stimulatory activity of BR on PC synthesis was arranged in the following order: BL ≫ 24-epiBL ≫ homoBL ≫ CS ≫ 24-epiCS ≫ homoCS.

Isolation and characterization of brassinosteroids from algal cultures of Chlorella vulgaris Beijerinck (Trebouxiophyceae)

The brassinosteroids (BRs) occur ubiquitously in the plant kingdom. The occurrence of BRs has been demonstrated in almost every part of higher plants, such as pollen, flower buds, fruits, seeds, vascular cambium, leaves, shoots and roots. In this study, BRs were isolated and identified in the culture of wild-type Chlorella vulgaris. Seven BRs, including teasterone, typhasterol, 6-deoxoteasterone, 6-deoxotyphasterol, 6-deoxocastasterone, castasterone and brassinolide, were identified by GC-MS. All compounds belong to the BR biosynthetic pathway. The results suggest that early and late C6 oxidation pathways are operating in C. vulgaris. This study represents the first isolation of BRs from C. vulgaris cultures.