Nutrient status and enzyme activity alteration in cucumber seedlings as a response to boron deficiency

Cucumber (Cucumus sativus L. var. Beit alpha) seedlings were grown in two groups on boron-deficient (traces of boron) and boron-sufficient (10.0 µM boron) hydroponic media for 30 days under controlled conditions. At harvest, the concentrations of magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) were determined in addition to boron (B) in the dry tissues of roots and leaves. The concentration of phenolic compounds in the roots was also determined. Peroxidase (POD) and catalase (CAT) enzyme activity was assayed in the fresh plant material. In addition, changes in the peroxidase and catalase isozyme patterns were also identified. The results showed that the vegetative growth of cucumber plants was negatively affected by boron deficiency. Biomass accumulation decreased by as much as 24.3% in the shoots and 49.1% in the roots. The nutrient concentrations in both the leaves and roots of B-stressed plants were substantially lower. Phenolic compounds were accumulated in significant amounts in the roots of deficient plants. The peroxidase and catalase enzyme activities were significantly increased in the tissues of deficient plants and new isozymes were induced or activated. The irregular biochemical changes occurring in B-deficient plants were explained as a plant physiological response to B-deficient conditions.

Fungitoxicidade, atividade elicitora de fitoalexinas e proteção de pepino contra Colletotrichum lagenarium, pelo extrato aquoso de Eucalyptus citriodora

Compostos secundários presentes em plantas medicinais podem desempenhar funções importantes em interações planta-patógeno, através de ação antimicrobiana direta ou ativando mecanismos de defesa de outras plantas que venham a ser tratadas com esses compostos. Com o objetivo de verificar o potencial de eucalipto (Eucalyptus citriodora) no controle alternativo de antracnose em pepino (Cucumus sativus), extrato aquoso (EA) desta essência florestal, autoclavado ou não autoclavado, nas concentrações de 0,1, 1, 5, 10, 15, 20 e 25% foi utilizado nos seguintes ensaios: indução de fitoalexinas em mesocótilos estiolados de sorgo (Sorghum bicolor) e em cotilédones de soja (Glycine max); fungitoxicidade in vitro sobre conídios de Colletotricum lagenarium; indução de resistência local ou sistêmica em plantas de pepino. Água e Bion foram utilizados como tratamentos controle. Os resultados indicaram que os EAs autoclavados e não autoclavados induziram a síntese de fitoalexinas em sorgo a partir da concentração de 1%. Em soja ocorreu síntese de gliceolina a partir de 10% e 15% dos EAs autoclavados e não autoclavados, respectivamente. Houve inibição total na germinação de esporos e formação de apressórios de C. lagenarium em concentrações de 20% e 1% do EA autoclavado, respectivamente. Para o extrato não autoclavado houve 75% de inibição da germinação de esporos em 25% do EA e inibição total da formação de apressórios em 15% do EA. Baseado no parâmetro tamanho de lesão, o extrato aquoso de E. citriodora, não autoclavado, apresenta potencial para induzir resistência local em pepino contra C. lagenarium.

Reversal of Fluridone-Reduced Chlorophyll Accumulation in Cucumber (Cucumus sativus) Cotyledons by Stimulatory Compounds

Pretreatment of etiolated cucumber cotyledons with potassium (K), benzyladenine (BA), or δ-aminolevulinic acid (ALA) for 20 h in the dark, followed by exposure to light for 24 h, increased chlorophyll and carotenoid content. A similar treatment with fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} decreased the levels of these photosynthetic pigments. However, when the etiolated cotyledons were pretreated with either BA or ALA for 20 h in the dark, followed by fluridone during a 24-h light period, the inhibitory effects of fluridone on chlorophyll content were reversed and the values were higher than the controls. In these treatments, ALA did not counteract the inhibitory effects of fluridone on carotenoids, but BA reduced the effects. In the cucumber cotyledon greening system, K was found to be most effective in stimulating both chlorophyll and carotenoid accumulation. When K was administered to the cotyledons either together with, prior to, or after the fluridone treatment, the inhibitory effect of fluridone on chlorophyll accumulation was totally eliminated and the stimulatory effects due to K were still maintained. Although K increased carotenoid content, it did not reverse the inhibitory effect of fluridone on carotenoids. From these findings it is concluded that the inhibition of chlorophyll and carotenoid accumulation by fluridone may be mediated via unrelated mechanisms at fluridone concentrations that do not totally eliminate or drastically reduce carotenoid content.

An Investigation on the Mechanism of Action of Propachlor

Studies were conducted to examine over time the effects of propachlor (2-chloro-N-isopropylacetanilide) on the growth of cucumber (Cucumus sativusL. ‘Straight Eight’) roots and associated biosynthetic reactions. Complete inhibition of root elongation occurred within 16 hr after exposure to propachlor. Inhibition of growth was not found to be a result of an effect on ATP formation or respiration. Protein biosynthesis was reduced several hours before the observed inhibition of growth therefore implicating it as the causal factor. Inhibition of protein synthesis occurred prior to an observed reduction in RNA synthesis suggesting that the primary effect of propachlor is on protein biosynthesis and that its effect on nucleic acid synthesis is secondary. It is concluded that the primary mechanism of action of propachlor is its effect on nascent protein biosynthesis.

Nucleic Acid and Protein Changes Induced by Auxin-Like Herbicides

Cucumber(Cucumus sativusL. ‘Chicago pickling’) and wheat(Triticum aestivumL. ‘Manitou’) seeds were germinated in various concentrations of (2,4-dichlorophenoxy) acetic acid (2,4-D), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloropicolinic acid (picloram). The nucleic acid and protein levels in the roots of the two species were determined 4 days after germination and compared on a per root basis. All four herbicides increased the DNA and protein of both cucumber and wheat roots with the increase in cucumber being higher than in wheat. The greatest difference between the tolerant wheat and susceptible cucumber was the effect on the RNA levels. As the concentration of all four herbicides increased, a progressive decrease of RNA levels occurred in wheat. In contrast, in cucumber the herbicides at high concentrations (10 and 100 ppmw) increased the RNA levels by more than 200% over the water controls. When the protein levels in both species were compared on a per unit RNA basis, there was an inverse relationship. In wheat the protein/RNA ratio was higher than the control whereas in cucumber the ratio was lower. A differential alteration of RNA species and interference with protein synthesis is suggested as the basis for selectivity.