Space and time in the plant cell wall (Viewpoint)
Effects of cell wall spacing, pH and heat on creep of sunflower hypocotyls reveal distinct extension processes operating over different timescales. These are taken by Thompson (pp. 203–211) to indicate tissue-specific cell wall behaviour in growing tissues, guard cells and abscission cells.
Seed recalcitrance (Review)
Metabolic activity of recalcitrant seeds with high water content is discussed by Berjak and Pammenter (pp. 213–228). It is a major factor underlying their desiccation sensitivity. Deficiencies in factors conferring desiccation tolerance contribute to the inability of recalcitrant seeds to tolerate slow dehydration. Drying rate is shown to be critical in achieving successful embryonic axis cryopreservation.
Ethylene and the submergence escape (Review)
Many species that succeed in flood-prone areas elongate their leaves or stems at an accelerated rate when submerged. Jackson (pp. 229–248) evaluates the evidence for invoking entrapped ethylene in this escape mechanism, reviews the physiological and molecular basis for the effect, and discusses likely directions of future work.
Differential abscission zone activation of Aux/IAA genes by two auxins
The auxin 2,4-D is more effective than NAA in reducing floret bud abscission in Cestrum elegans cut flowers (Abebie et al., pp. 249–259). Use of differential activation of six Ce-Aux/IAA genes as a measure of free-auxin levels shows that effectiveness can be related to the extent of acropetal auxin transport.
Broomrape controls IAA flow during infection of its host
Broomrape (Orobanche aegyptiaca) is shown to manipulate its host by acting as a sink for auxin (IAA). Based on infection characteristics in Arabidopsis thaliana, Bar-Nunet al.(pp. 261–265) suggest that disrupting IAA action or flow by chemical means is a promising approach for controlling infection in the field.
DNA repair in seeds and pollen at Chernobyl
Boubriak et al. (pp. 267–276) report DNA repair and adaptation in pollen and embryos from Betula verrucosa and Oenothera biennis growing in different radionuclide fall-out sites around Chernobyl exposed to chronic γ/β irradiation. At sites with high levels of α-emitters, DNA repair still remains impaired.
Surface mucilage helps repair embryo DNA of desert-adapted seeds
Repair of damaged DNA of seed embryos of two species of Artemisia is demonstrated by Huang et al. (pp. 277–283) to be promoted by hydration from dew captured during the desert night by pectinaceous surface mucilage.
Abscission-zone cells as ethylene targets
McManus (pp. 285–292) shows that the separation process of leaf abscission requires the generation of a signal (or signals) from remote tissues that act in concert with ethylene. Once evoked, abscission cells maintain a developmental memory such that control mechanisms mediated by ethylene/auxin prior to separation are retained by the cells after separation.
Seed germination strategy of an inland xero-halophyte
Seed germination is critical for survival in salt deserts. Qu et al. (pp. 293–299) show that seed and early seedling stages of Halocnemum strobilaceum are highly salt tolerant. Physiological responses typical of the Mediterranean salt steppe of Spain are found to differ from those of the inland cold salt desert of north-west China.
Ethylene influences on senescence and necrosis
Using transgenic Nicotiana sylvestris plants exhibiting a silenced or constitutive ethylene response, Yang et al. (pp. 301–310) show the gas to play an important role in organ senescence and tissue necrosis. This novel material is a useful resource for exploring how senescence processes are regulated in plants.