Stage of harvest and polyunsaturated essential fatty acid concentrations in purslane (Portulaca oleraceae) leaves.

Purslane is a nutritious vegetable crop rich in the polyunsaturated essential fatty acids (PUEFA) alpha-linolenic acid (LNA) and linoleic acid (LA), which are essential for normal human growth, health promotion, and disease prevention. Total lipids and fatty acid concentrations at three stages of harvest (6-, 10-, and 14-true-leaf stages) were examined in a cultivated variety of purslane (Portulaca oleraceae L. var. sativa). The 14-true-leaf stage of growth was found to be ideal for harvest because at this stage the leaf area, shoot fresh weight, shoot dry weight, and PUEFA concentrations per gram of leaf fresh weight were higher (P < or = 0.05) than at the 6- and 10-true-leaf stages of growth. The LNA to LA ratio was also highest at the 14-true-leaf stage.

Influence of ionic thiocyanate on growth of cabbage, bean, and tobacco.

Plant weight and contents of chlorophyll, ionic thiocyanate (SCN(-)), and hydrogen cyanide (HCN) were determined in cabbage (Brassica oleracea var.capitula L. cv. Early Greenball), bean (Phaseolus vulgaris L. cv. Contender), and tobacco (Nicotiana tabacum L. cv. Delhi 76) grown hydroponically in modified Hoagland's nutrient solution with six concentrations of SCN(-) (supplied as KSCN) (0, 5, 25, 50, 100, and 200 mg/liter). Whereas tobacco plants did not grow with any level of SCN(-) in the culture solution, beans grew with 5 mg/liter and cabbages grew with between 5 and 50 mg/ liter. Increasing levels of SCN(-) in the culture solution resulted in decreased growth and chlorophyll content, accompanied by consistently increasing amounts of SCN(-) in cabbage. Small amounts of HCN found only in tissues of cabbage were not influenced by levels of SCN(-). The greater insensitivity of cabbages to the presence of SCN(-) compared with beans is apparently related to the presence of endogenous glucosinolates which are capable of being degraded into SCN(-). Accumulation of SCN(-) and occurrence of leaf chlorosis in cabbage and beans and death of tobacco plants supplied with SCN(-) in hydroponic culture confirm the capacity of SCN(-) as an allelopathic agent, but its effect mechanism in ecology needs to be demonstrated.