No abstract

Dormant or quiescent buds of woody perennials are often dense and in the case of grapevine (Vitis vinifera L.) have a low tissue oxygen status. The precise timing of the decision to resume growth is difficult to predict, but once committed, the increase in tissue oxygen status is rapid and developmentally regulated. Here, we show that more than a third of the grapevine homologues of widely conserved hypoxia-responsive genes and nearly a fifth of all grapevine genes possessing a plant hypoxia-responsive promoter element were differentially regulated during bud burst, in apparent harmony with resumption of meristem identity and cell-cycle gene regulation. We then investigated the molecular and biochemical properties of the grapevine ERF-VII homologues, which in other species are oxygen labile and function in transcriptional regulation of hypoxia-responsive genes. Each of the 3 VvERF-VIIs were substrates for oxygen-dependent proteolysis in vitro, as a function of the N-terminal cysteine. Collectively, these data support an important developmental function of oxygen-dependent signalling in determining the timing and effective coordination bud burst in grapevine. In addition, novel regulators, including GASA-, TCP-, MYB3R-, PLT-, and WUS-like transcription factors, were identified as hallmarks of the orderly and functional resumption of growth following quiescence in buds.

A technique was devised to measure the internal turgor pressure required for fruit rupture in order to assess resistance to splitting objectively rather than rely solely on field observation. In the laboratory, fruit of uniform maturity and known osmotic potential were immersed in a range of osmotica to create a known turgor pressure at equilibrium. "Critical turgor", the pressure which resulted in 50% of the berries splitting, was approximately 15 atm in grape cultivars prone to splitting and 40 atm in resistant cultivars. Cultural treatments with growth regulators subsequently affected fruit resilience. p-Chlorophenoxyacetic acid lowered critical turgor, while gibberellic acid caused an increase. These laboratory-based observations coincided with field experience. Additional factors in fruit splitting, including berry morphology and anatomy, are discussed.

Background and Aims Plants regulate cellular oxygen partial pressures (pO2), together with reduction/oxidation (redox) state in order to manage rapid developmental transitions such as bud burst after a period of quiescence. However, our understanding of pO2 regulation in complex meristematic organs such as buds is incomplete and, in particular, lacks spatial resolution.Methods The gradients in pO2 from the outer scales to the primary meristem complex were measured in grapevine (Vitis vinifera) buds, together with respiratory CO2 production rates and the accumulation of superoxide and hydrogen peroxide, from ecodormancy through the first 72 h preceding bud burst, triggered by the transition from low to ambient temperatures.Key Results Steep internal pO2 gradients were measured in dormant buds with values as low as 2·5 kPa found in the core of the bud prior to bud burst. Respiratory CO2 production rates increased soon after the transition from low to ambient temperatures and the bud tissues gradually became oxygenated in a patterned process. Within 3 h of the transition to ambient temperatures, superoxide accumulation was observed in the cambial meristem, co-localizing with lignified cellulose associated with pro-vascular tissues. Thereafter, superoxide accumulated in other areas subtending the apical meristem complex, in the absence of significant hydrogen peroxide accumulation, except in the cambial meristem. By 72 h, the internal pO2 gradient showed a biphasic profile, where the minimum pO2 was external to the core of the bud complex.Conclusions Spatial and temporal control of the tissue oxygen environment occurs within quiescent buds, and the transition from quiescence to bud burst is accompanied by a regulated relaxation of the hypoxic state and accumulation of reactive oxygen species within the developing cambium and vascular tissues of the heterotrophic grapevine buds.

Microsporogenesis was studiedin eleven Actinidia taxa including A. deliciosa (kiwifruit) and in an interspecific hybrid. From chromosome counts at meiotic metaphase 1 or diakinesis, eight taxa were classified as diploids and two as tetraploids and A. deliciosa was confirmed as hexaploid. A putative 2n = 2x, 2n = 4x, 2n = 6x, x = 29 basis for the genus is therefore supported. Chromosomes in all taxa were very small. Three diploids and two polyploids analysed for meiotic pairing behaviour were all characterised by low chiasma frequencies per bivalent. Chromosome configurations other than bivalents were rare in A. arguta var. arguta (4x) and A. deliciosa (6x), indicating there may be genetic control ofchiasmata distribution in these polyploids.