Differential callus type formation by auxins and cytokinin in in vitro cultures of pepper (Capsicum annuum L.)

ABSTRACT

Two types of callus were produced by pepper explants cultured in various media containing auxins, the cytokinin 6-benzylaminopurine (BAP) and the auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA). Callus produced on media containing auxins alone was friable, grey-green or green-orange in colour and more compact, whereas when BAP was added to culture media with a low concentration of auxin or when the medium contained TIBA alone, the callus produced was white and very hard. This type of callus was also produced in cultures of older tissues and of young tissues cultured on hormonefree medium. Results are discussed in relation to the role of cytokinins in wounding, phenylpropanoid metabolism and lignin biosynthesis.     

Secondary wall deposition in tracheary elements of cucumber grown in vitro

It is a matter of controversy whether secondary wall deposition is dependent on lignification during the development of tracheary elements. To understand this, tracheary element differentiation was studied in the homogeneous calli obtained from the cotyledonary explants of Cucumis sativus subsequent to treatment with plant growth regulators, such as naphthalene acetic acid (NAA) and benzylamino purine (BAP), which are necessary for the induction of tracheary elements, along with metabolic blockers such as 2-aminoindan-2-phosphonic acid (AIP), 2,3,5-triiodobenzoic acid (TIBA) and nifedipine. Calli treated with AIP, a potential inhibitor of L-phenylalanine ammonia-lyase (PAL), have no PAL activity at any time during the culture period. There was a complete inhibition of lignification although secondary wall deposition was unaltered. Similar results were obtained using TIBA, an inhibitor of auxin transport, and nifedipine, a known calcium channel blocker. Thus the present study suggests that secondary wall deposition in the course of tracheary element differentiation need not to be dependent on lignification. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of plant growth regulators on flowering,fruiting, seed oil content,and oil quality of Jatropha curcas

Field experiments were conducted to determine the effects that plant growth regulators (PGRs) have on seed production of Jatropha curcas when they are used for chemical pruning. In the subsequent year, following a single foliar application of PGRs, flowering, fruit set, fruit characteristics, seed total oil content and oil free fatty acid (FFA) content were evaluated. The number of flowers per plant, number of fruits per bunch, fruit- and seed characteristics and seed oil content were significantly affected by the different treatments. However, there were no variations in the degree of fruit set or oil FFA content. A single foliar application of N⁶-benzyladenine produced more flowers per plant, more fruits per bunch, heavier and bigger fruits and seeds with more oil compared to manual pruning. Treatment with 2,3,5-triiodobenzoic acid yielded more flowers per plant and heavier fruits with a higher oil content than the control and manually pruned plants. Treatment with 2,3:4,6-di-O-isopropylidene-2-keto-l-gulonic acid yielded similar results. More fruits per bunch and more seeds per fruit were also produced. Maleic hydrazide treatment yielded more flowers per plant, heavier and bigger fruits with more, heavier, oil rich seeds compared to the control and manual pruning. This study indicates that foliar application of PGRs as chemical pruners in J. curcas may have a sequential effect in boosting seed production, seed oil content and improves fruit quality.     

Shoot multiplication in cultures of mature <Emphasis Type="Italic">Alnus glutinosa</Emphasis>

Shoot cultures were initiated from mature trees of Alnus glutinosa. On medium containing 1–5 μM 6-benzylamino purine (BAP), the shoots elongated without branching, formed heavy callus at the base of the stems and readily formed roots. The possibility that these characteristics could be attributed to the strong influence of endogenous auxin was tested on media that contained two auxin transport inhibitors, 1-N- naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), at concentrations of 0.1–3 μM, in combination with 2 μM BAP. On these media, shoots produced numerous branches, less callus and no roots. After 30 weeks (five subcultures) on this medium, leaves were smaller and showed signs of vitrification. These problems were resolved without detriment to shoot proliferation, by reverting to medium without NPA or TIBA. Shoots rooted readily after transfer to medium without growth regulators and were successfully acclimatised after transfer to soil.     

The regulation of sweet cherry fruit abscission by polar auxin transport

Inconsistency of cropping is an important problem for UK sweet cherry production. Premature fruit abscission in Prunus can reduce yields severely, however, the environmental cues and hormonal signals that trigger abscission have not been identified. Auxin (IAA) is known to delay abscission by reducing the sensitivity of cells in the abscission zone to ethylene, a promoter of abscission. Therefore, the capacity for polar auxin transport (PAT) through sweet cherry pedicels was examined in relation to fruit abscission. Cherry ‘spurs’ (short shoots) with similar leaf areas and different fruit numbers were phloem-girdled to restrict assimilate movement. Abscission from spurs with many fruit (eight or more) occurred within 14 days of girdling, whereas abscission from spurs with few (two) fruit was minimal. The pedicels’ capacity for PAT in spurs with different fruit numbers was determined 1, 3 and 9 days after girdling (DAG). Fruit were analysed for endogenous IAA concentration 3, 5, 7 and 9 DAG. PAT inhibitors 2,3,5-triiodobenzoic acid or 1-N-naphthylphtalamic acid were applied to pedicels of fruit not expected to abscise, i.e. on spurs with few fruit. The effect of these inhibitors on fruit abscission was determined 14 DAG. The proportion of the transported [³H]-IAA was lower from the outset in pedicels from spurs with many fruit. By 9 DAG, symptoms of fruit abscission were apparent and 40% less [³H] -IAA was transported through pedicels on spurs with many fruit. Fruit endogenous IAA concentrations were similar in the two groups of spurs. Application of PAT inhibitors shortly after girdling increased fruit abscission by 30%. The results suggest that although a decline in PAT is not the only cause of fruit abscission, the maintenance of PAT contributes to fruit retention.     

The PIN1 family gene PvPIN1 is involved in auxin-dependent root emergence and tillering in switchgrass

Switchgrass (Panicum virgatum L.; family Poaceae) is a warm-season C4 perennial grass. Tillering plays an important role in determining the morphology of aboveground parts and the final biomass yield of switchgrass. Auxin distribution in plants can affect a variety of important growth and developmental processes, including the regulation of shoot and root branching, plant resistance and biological yield. Auxin transport and gradients in plants are mediated by influx and efflux carriers. PvPIN1, a switchgrass PIN1-like gene that is involved in regulating polar transport, is a putative auxin efflux carrier. Neighbor-joining analysis using sequences deposited in NCBI databases showed that the PvPIN1gene belongs to the PIN1 family and is evolutionarily closer to the Oryza sativa japonica group. Tiller emergence and development was significantly promoted in plants subjected toPvPIN1 RNA interference (RNAi), which yielded a phenotype similar to that of wild-type plants treated with the auxin transport inhibitor TIBA (2,3,5-triiodobenzoic acid). A transgenic approach that inducedPvPIN1 gene overexpression or suppression altered tiller number and the shoot/root ratio. These data suggest that PvPIN1plays an important role in auxin-dependent adventitious root emergence and tillering.     

Adventitious Bud Formation from Bulb-scale Explants of Lilium speciosum Thunb. in vitro Effects of aminoethoxyvinyl-glycine, 1-aminocyclopropane-1-carboxylic acid,and ethylene

Several representatives of marine brown macroalgae (Phaeophyceae) including Fucus serratus L., Fucus spiralis L. and Fucus vesiculosus L. as well as Laminaria digitata (Huds.) Lamour., Laminaria hyperborea (Gunn.) Foslie and Laminaria saccharina (L.) Lamour. were investigated with particular regard to features of biosynthesis of the storage product mannitol. The respective catalytic system involved in the last step of mannitol formation, mannitol-1-phosphate dehydrogenase, appears to be a cytoplasmic enzyme as may be judged from the degree of correlation with the chloroplast key enzyme ribulose-1,5-bisphosphate carboxylase in different tissues of Laminaria digitata and Laminaria saccharina. Activity of mannitol-1-phosphate dehydrogenase in vitro is not affected by mannitol-l-phosphate or free mannitol, suggesting that mannitol biosynthesis in vivo) is mainly controlled by the environment and/or developmental stage. Certain inorganic ions such as NO₃^- (including K⁺) exert a strong influence on the activity of mannitol1-phosphate dehydrogenase thus suggesting that the intracellular pools of stored NO₃^- and mannitol are confined to spatially separated cellular compartments.