Showing papers by "Anita Solar published in 2014"

Novel Roles for the Polyphenol Oxidase Enzyme in Secondary Metabolism and the Regulation of Cell Death in Walnut

Abstract: The enzyme polyphenol oxidase (PPO) catalyzes the oxidation of phenolic compounds into highly reactive quinones. Polymerization of PPO-derived quinones causes the postharvest browning of cut or bruised fruit, but the native physiological functions of PPOs in undamaged, intact plant cells are not well understood. Walnut (Juglans regia) produces a rich array of phenolic compounds and possesses a single PPO enzyme, rendering it an ideal model to study PPO. We generated a series of PPO-silenced transgenic walnut lines that display less than 5% of wild-type PPO activity. Strikingly, the PPO-silenced plants developed spontaneous necrotic lesions on their leaves in the absence of pathogen challenge (i.e. a lesion mimic phenotype). To gain a clearer perspective on the potential functions of PPO and its possible connection to cell death, we compared the leaf transcriptomes and metabolomes of wild-type and PPO-silenced plants. Silencing of PPO caused major alterations in the metabolism of phenolic compounds and their derivatives (e.g. coumaric acid and catechin) and in the expression of phenylpropanoid pathway genes. Several observed metabolic changes point to a direct role for PPO in the metabolism of tyrosine and in the biosynthesis of the hydroxycoumarin esculetin in vivo. In addition, PPO-silenced plants displayed massive (9-fold) increases in the tyrosine-derived metabolite tyramine, whose exogenous application elicits cell death in walnut and several other plant species. Overall, these results suggest that PPO plays a novel and fundamental role in secondary metabolism and acts as an indirect regulator of cell death in walnut.

‘Sava’ and ‘Krka’ Walnut Cultivars

Abstract: ‘Sava’ and ‘Krka’ are new walnut cultivars of Slovene origin. They were developed and evaluated at the Biotechnical Faculty Ljubljana, Slovenia, and were released in 2013. ‘Sava’ is a late-leafing cultivar, appropriate for orchard planting in continental climatic conditions. It has good and regular crop, owing to an intermediate fruiting pattern and good balance between vegetative growth and fruiting. As the homogamous cultivar, ‘Krka’ is suited for home gardens as a solitary tree that forms a densely branched canopy with a rather erect to spreading growth habit and lateral fruiting pattern. As a result of its good yielding capacity, it is also recommended for orchard planting in warmer areas.