Cyclofarnesoids and methylhexanoids produced from β-carotene in Phycomyces blakesleeanus

The oxidative cleavage of β-carotene in the Mucorales produces three fragments of 18, 15, and 7 carbons, respective heads of three families of apocarotenoids: the methylhexanoids, the trisporoids, and the cyclofarnesoids (named after their 1,6-cyclofarnesane skeleton). The apocarotenoids are easily recognized because they are absent in white mutants unable to produce β-carotene. In cultures of Phycomyces blakesleeanus we detected thirty-two apocarotenoids by LC, UV absorbance, and MS. With additional IR and NMR we identified two methylhexanoids and the eight most abundant cyclofarnesoids. Four of them were previously-unknown natural compounds, including 4-dihydrocyclofarnesine S, the most abundant cyclofarnesoid in young cultures. We arranged the apocarotenoids of the Mucorales in a scheme that helps classifying and naming them and suggests possible metabolites and biosynthetic pathways. We propose specific biosynthetic pathways for cyclofarnesoids and methylhexanoids based on structural comparisons, the time course of appearance of individual compounds, and the bioconversion of β-apo-12-carotenol, an early precursor, to three more oxygenated cyclofarnesoids by the white mutants. Some of the reactions occur spontaneously in the increasingly acidic culture media. Mating increased the contents of methylhexanoids and cyclofarnesoids by ca. threefold in young cultures and ca. twelvefold in old ones (five days); cyclofarnesine S, the most abundant cyclofarnesoid in old cultures, increased over one hundredfold. We found no differences between the sexes and no activity as sexual pheromones, but we suggest that methylhexanoids and cyclofarnesoids could mediate species-specific physiology and behavior.

The capacity of antioxidant protection during modulated ageing of bean (Phaseolus vulgaris L.) cotyledons. 2. The low-molecular weight antioxidants

The aim of the present work was to evaluate non-enzymic antioxidants during natural and artificially modulated senescence. Senescence of bean (Phaseolus vulgaris L. cv. Jantar) cotyledons was modulated by UV C irradiation or by the decapitation of plants apices. The content of beta-carotene and zeaxanthin decreased in control and decapitated plants but in UV C irradiated plants these contents increased. The degree of de-epoxidation increased in all cultivations with age. The content of total glutathione (sum of reduced and oxidized) sharply decreased in bean cotyledons grown in all conditions. Interestingly, the content of total ascorbate increased at the end of cotyledon life span of control and decapitated plants but decreased in UV plants. Decrease of reduced/oxidized ratio of ascorbate and glutathione during cotyledon ageing confirmed increasing oxidative stress during senescence in all cultivations.

The capacity of antioxidant protection during modulated ageing of bean (Phaseolus vulgaris L.) cotyledons. 1. The antioxidant enzyme activities

Reactive oxygen species are known to increase in plant senescence. We investigated the participation of antioxidative enzymes in initiation of cotyledon senescence. Senescence of bean (Phaseolus vulgaris L.) cotyledons was modulated by UV C irradiation and by the decapitation of plant apices. Senescence was accompanied by a decrease of protein content and by a decrease of photochemical efficiency. A drop in activity of antioxidative enzymes preceded the onset of senescence in control plants. In cotyledons with prolonged life span, the decrease of antioxidant activities and the markers of senescence onset appeared at a similar age as in controls. Thus we presumed that the period from senescence initiation to cotyledon abscission was extended. On the other hand, in UV C irradiated plants we did not observe actual senescence initiation, and antioxidant enzymes although elevated, did not effectively play their role. The decrease of antioxidant enzymes activity and the markers of senescence appeared at a similar age both in control and in decapitated (D) plants, so we can presume that we prolonged mainly the period from senescence onset to cotyledon abscission in D plants. In UV C irradiated plants the antioxidative enzymes were probably destroyed before the process of senescence could begin.