Plant Growth Regulation

The frequencies of adventitious root formation in vitro of isolated shoots from bud cultures of apple (Malus pumila cv. Jonathan) after 1, 7 and 31 subcultures (weeks 5, 29 and 109 after the initial culture) were 5, 78 and 95% respectively. Endogenous gibberellin-like substances (GA) were extracted, chromatographed on SiO2 partition columns, and assayed on dwarf rice (Oryza sativa cv. Tan-ginbozu). The levels of GA in shoots from the 1st, 7th and 31st subcultures were 40, 19 and 14 ng GA3 eq./g dry weight of tissue, respectively, a trend which suggests an inverse relationship between endogenous GA level and rooting ability. This is consistent with the fact that applied GA3 inhibits rooting in apple and many other species. The major peak of GA activity eluted coincidentally with GA1/GA3/GA19. Endogenous cytokinin-like substances (CK) were chromatographed on paper and assayed with soybean hypocotyl sections. In contrast to the decrease in GA activity, CK activity increased 1.5–2.7 fold in the later subcultures (cytokinin activity per shoot, however, declined).

Poor seedling establishment is a major deterrent in adopting direct seeding of rice. Seed priming to obtain better crop stand could be an attractive approach. The objective of this study was to determine the effectiveness of seed priming strategies on the improved agronomic characters of direct-sown rice. Seed priming strategies were: hydropriming for 48 h, osmohardening with KCl or CaCl2 for 24 h, ascorbate priming for 48 h and seed hardening for 24 h, pre-germination (traditional soaking for nursery raising) and untreated control. Seed priming improved germination and emergence, allometry, kernel yield, and its quality, whilst pre-germination displayed poor and erratic emergence of seedling followed by poor plant performance. Faster and uniform emergence was due to improved α-amylase activity, which increased the level of soluble sugars in the primed kernels. Osmohardening with KCl gave greater kernel and straw yield and harvest index, followed by that of CaCl2, hardening and ascorbate priming. Improved yield was attributed principally to number of fertile tillers and 1000 kernel weight. A positive correlation between mean emergence time and days to heading, while a negative one between kernel yield and harvest index suggested long-term effects of seed priming on plant growth and development. The results suggest that physiological changes produced by osmohardening enhanced the starch hydrolysis and made more sugars available for embryo growth, vigorous seedling production and, later on, improved allometric, kernel yield and quality attributes.

The effect of cycloheximide (CH) on the indol-3yl-acetic acid (IAA)-stimulated transport of 14C-labelled abscisic acid (ABA) and 14C-labelled sucrose was studied in 110 mm long pea epicotyl segments. IAA application resulted in elongation growth of the segments. This effect was decreased by CH treatment which also reduced [14C] ABA and [14C] sucrose accumulation in the growing apical part of the segments. A reduction in [14C] IAA uptake and in protein synthesis in this part of the segments was also observed. The simultaneous inhibition of protein synthesis and reduction of [14C] ABA and [14C] sucrose transport suggests that IAA can stimulate the transport of ABA and sucrose through a protein synthesis-based elongation growth.

The gasotransmitter, hydrogen sulfide (H2S) is involved in plant growth and development, and stress responses. Plant hormones influence the levels of endogenous H2S and H2S may affect the biosynthesis, transport, and signal transduction of different phytohormones. The dual role of H2S in the interaction with phytohormones contributes to the physiological functions of H2S in the life cycle and responses to abiotic stresses in plants. The biological effect of H2S might depend on the ratio between phytohormones. However, the mechanism by which H2S and plant hormones interplay in plants remains fragmentary. This review summarized the biosynthesis and degradation of H2S and discussed the cross-talk between H2S and different phytohormones along with the future perspectives.

In eggplant microspore embryogenesis, embryos are produced and then transformed into undifferentiated calli, instead of developing as true embryos. This is the main current bottleneck that precludes this process from being efficient. In this work we aimed to shed light on the factors involved in the successful in vitro development of eggplant haploid embryos by evaluating the role of growth regulators (GRs) in this process. We analyzed the endogenous levels of different GRs, including auxins, cytokinins and gibberelins, as well as salicylic, jasmonic and abscisic acid, in microspores and microspore-derived embryos at different culture stages. We also analyzed the same GR profiles in leaf and anther wall tissues of different eggplant backgrounds. Finally, we assessed the application of different GR combinations to the culture medium. Our results showed that in eggplant there are no genotype-specific endogenous GR profiles that can be associated to a high embryogenic response. Instead, the embryogenic response seems related to different GR accumulation patterns during in vitro culture. The changes observed in the endogenous levels of salicylic and abscisic acid were not related to the embryo transition. There were, however, changes in the levels of indole acetic acid and dihydrozeatin. The best GR combination to promote callus production was 0.5 mg/L 1-naphthaleneacetic acid (NAA) and 0.5 mg/L 6-benzylaminopurine (BAP). A 20% reduction of NAA and BAP reduced embryo production but produced structures more anatomically similar to embryos. These results shed light on the role of GRs during the development of microspore-derived embryos in eggplant microspore cultures.

Culturing a non-habituated cell line of Fagara zanthoxyloides Lam. (Rutaceae) in either auxin-free medium or cytokinin-free medium led to opposite effects on furoquinoline accumulation. It appeared that production of skimmianine and γ-fagarine in the cells was strongly correlated with the presence of exogenous BAP: the levels of both alkaloids were 9 times lower when cells were cultured without cytokinin than in the control culture. NAA removal induced a slight stimulation of skimmianine and γ-fagarine accumulations, 1.2 and 1.9 times respectively. Culturing the cells in a PGR-free medium generated skimmianine and γ-fagarine levels that were 3.5 and 2.1 times lower, respectively, confirming the opposite effects of BAP and NAA on furoquinoline accumulation. Growth was only slightly inhibited when cells were cultured for one passage in the PGR-modified media.

Mass spectra provide definitive identification of indole-3-acetic acid and abscisic acid in shoots of Coleus blumei, a species used for studying the hormone control of plant development since the early 1930s.

Xerophyta humilis (Bak.) Dur. and Schinz is a poikilochlorophyllous resurrection plant in that it is tolerant of considerable water loss (< 5% relative water content [RWC]) and thylakoid membranes are dismantled and chlorophyll is lost during dehydration. In this paper we examined the processes associated with recovery from desiccation upon rehydration. Dried leaf explants were rehydrated in water (control) or in solutions of actinomycin-D or cyclohexamide in order to determine to what extent initial recovery was dependant on de novo transcription and translation respectively. Our results suggest that considerable protection of subcellular organisation and components of metabolism occurs during drying such that the initial recovery of metabolism on rehydration is virtually independent of de novo transcription of nuclear genes. However recovery does require the synthesis of new proteins. The plasmalemma remains intact and macromolecular synthesis is not required for maintenance of its integrity. Messenger RNA's for chlorophyll biosynthesis appear to be stored in a stable form in the dried leaves and are translated on rehydration. Similarly most of the mRNA's necessary for recovery of electron transport in the chloroplast (as determined by measuring the quantum efficiency of photosystem II [FV/FM] using chlorophyll fluorescence) appear to be stabily present in the dried leaves. However, for total recovery of FV/FM new genomic transcription is necessary.

Plants have been regenerated from petiole explants of six elite sugar beet (Beta vulgaris L.) cultivars. Significant variation was found between the responses of the six cultivars to elevated temperature and the N6-benzyladenine concentrations evaluated. The importance of genotype in the regeneration of plantlets from sugar beet petiole explants is considered.