ENVIRONMENTAL CONTROL . . . . . . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Genetics of Sensitivity to Environmental Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control by Day Length . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Control of floral evocation and morphogenesis

Publisher Summary The chapter presents a discussion on plant growth-regulating (PGR) substances in the rhizosphere, with emphasis on microbial production and functions. The chapter discusses the rhizosphere as a site of plant-microbe interactions; plant growth-regulating substances and their sources; biochemistry of microbial production of PGRs; production of PGRs by rhizosphere microorganisms; metabolism of PGRs in soil; and ecological significance of PGRs produced in the rhizosphere. The chapter provides a better understanding of the mechanisms of actions of microbially derived PGRs and their interactions with plants. Moreover, development of hormone-deficient plant mutants can provide opportunities to clearly define the role of microbially produced PGRs in plan-microbe interactions. An understanding of these aspects can aid in the utilization of microbial PGRs for the betterment and benefit of sustainable agriculture.

Plant growth-regulating substances in the rhizosphere: microbial production and functions

Potatoes (tubers of Solanum tuberosum ) are grown and eaten in more countries than any other crop, and in the global economy they are the fourth most important crop after the three cereals maize, rice, and wheat. Therefore, research into potato tuber initiation and development, which enables our

Multiple Signaling Pathways Control Tuber Induction in Potato

Continuing loss of native orchid habitat has lead to an increased emphasis on orchid conservation. Major obstacles in the production of native orchid seedlings for use in conservation have been: (1) development of efficient and reliable seed germination protocols and (2) an understanding of early seedling growth and development. Effects of six asymbiotic media (Modified Lucke, Murashige & Skoog, Lindemann, Vacin & Went, Malmgren Modified, Knudson C), four exogenous cytokinins (BA, Zea, Kin, 2-iP), and three photoperiods (0/24, 16/8, 24/0 h L/D) were examined on seed germination and early protocorm development of Habenaria macroceratitis, a rare native Florida terrestrial orchid. Finally, the effects of three photoperiods (8/16, 12/12, 16/8 h L/D) on in vitro seedling development were examined. Percent seed germination was highest on both LM and KC after seven weeks culture (LM = 89.1%, KC = 89.2%); however, protocorm development was enhanced on MM after both seven and 16 weeks. Both zeatin and kinetin at 1 µM enhanced seed germination (Zea = 58.1%, Kin = 47.2%). Final percent seed germination (91.7%) and protocorm development (Stage 4) was increased in the absence of light (0/24 h L/D). In␣vitro seedlings cultured under 8/16 h L/D conditions produced the highest number of tubers per seedling (1.06) with the greatest tuber (42.7 µg) and shoot (fwt = 69.5 µg) biomass and tuber diameter (3.1 mm).

http://hort.ufl.edu/plant-restoration/kane-lab/orchids/pdf/articles/18-stewart-2006-asymbiotic-germination-habenaria-macroceratitis.pdf

Asymbiotic seed germination and in vitro seedling development of Habenaria macroceratitis (Orchidaceae), a rare Florida terrestrial orchid

A plant embryo consists of an embryonic axis, which eventually grows into the adult body, and one or two nutritive structures, the cotyledons. In the grasses embryo morphogenesis can be divided into three periods: during the first the embryo is regionalized into an embryo proper and suspensor, during the second the embryonic axis is established, and during the third vegetative structures are elaborated. Maize, with its well-characterized embryo-genesis, powerful genetics, and transposon tagging stocks, offers an attractive system for mutational analysis of these events. We have isolated 51 embryo-specific (emb) mutations from active Robertson's Mutator maize stocks. These are single-gene recessive lethals that represent at least 45 independent mutation events. Each of the 25 mutations was located to a chromosome arm using a B-A translocation set that uncovers approximately 40% of the genome; the same test failed to locate 20 others. The embryo phenotype of 27 mutations was characterized by examining mature mutant embryos in fresh dissection: the various emb mutations differ in phenotype and each is consistent in its expression. All 27 mutations result in retarded embryos that are morphologically abnormal. Nine mutants are blocked during the first period; 10 mutants are blocked during the second period; and eight mutants are blocked during the third period. Based on both the genetic and developmental data, it is likely that there are many loci that can mutate to give the emb phenotype and that these genes are crucial to the morphogenesis of the embryo.

/pdf/isolation-and-characterization-of-51-embryo-specific-3vz6thibu4.pdf

Isolation and Characterization of 51 embryo-specific Mutations of Maize.

Some lines of Solanum tuberosum ssp. andigena are strictly photoperiodic, forming tubers only in short days and flowers only in long days. We used this advantageous phenomenon to study phytohormone involvement in the development of the plants, mainly that of tuber formation. Plants grown for 2 months under short days (SD) of 14 h darkness, night break (1 h white light in the middle of the 14-h dark period) and continuous light (LD) were compared. Short day-grown plants formed tubers, while plants in LD flowered. Night break prevented tuber formation, but caused flowering, although it was weaker than in LD. Plants grown under night break displayed many growth characteristics intermediate between SD and LD. Under LD and night break regimes ABA levels in all organs were about one-fourth of those under SD. An opposite trend was found for gibberellin content: it was very low in SD-grown plants and 4-10 times higher under both other conditions with the exception of roots and stolons in night break. Thus, the ratio of ABA/GA, known to be important for tuber formation, was high in SD and low in night break and LD. The level of free indoleacetic acid (IAA) was high in LD- and night break-grown plants and it was much lower in SD-grown plants, including tubers. Cytokinin (CK) levels were also high in LD- and night break-grown plants. In SD, leaves had slightly decreased and stems and roots + stolons had more pronouncedly decreased cytokinin levels. The CK/IAA ratio was thus higher in SD in stems and roots + stolons; it was also high in tubers and no difference was found in leaves. These results indicate that the effect of photoperiod on tuber formation and development may be mediated by photoperiod-induced changes in hormone levels.

Photoperiodic control of growth, development and phytohormone balance in Solanum tuberosum

We studied the interaction of the day length, cytokinins, and gibberellins in the control of tuberization in potato (Solanum tuberosum L, cv. Desire) plants and derived transgenic plants with the inserted PHYB gene from Arabidopsis encoding the synthesis of phytochrome B apoprotein and put under the control of the 35S CaMV promoter. Plantlets were cultured in vitro on hormone-free MS medium containing 5% sucrose and kinetin (1 mg/l) or/and GA (0.5 and 1.0 mg/l), at long day (LD, a 16-h photoperiod), short day (SD, a 10-h photoperiod), or continuous darkness conditions. The content of cytokinins (Ck, zeatin, and zeatin riboside) in various plant organs was determined by the immunoenzyme method, and GA activity was measured in bioassay with dwarf pea. Potato plant transformation with the PHYB gene enhanced substantially tuber initiation inhibition by LD. Kinetin addition to culture medium enhanced tuberization and reduced Ck content in aboveground shoots and Ck redistribution in the favor of underground organs. GA addition to the culture medium suppressed tuberization and induced Ck accumulation in aboveground organs. We concluded that Ck role in tuberization depends on their predominant localization in above- or underground potato organs. The involvement of Ck and GA in the competitive relations between growing tubers and shoots is considered.

Interaction between day length and phytohormones in the control of potato tuberization in the in vitro culture

Agrobacterium tumefaciens binary vectors carrying kanamycin resistance gene and either C58 T-DNA gene 4 for cytokinin synthesis or genes 1 and 2 for auxin synthesis were constructed and used for transformation of a short-day tobacco Maryland Mammoth Kanamycin resistant plants were regenerated from a small fraction of transformed tissue and the presence of T-DNA in their genome was verified by Southern blotting The level of endogenous cytokinin in plants transgenic for gene 4 and the level of endogenous IAA in those transgenic for genes 1 and 2 increased by more than 100 % A number of morphological characteristics distinguish them from untransformed controls

Transgenic tobacco plants with T-DNA phytohormone synthesis genes

Flowering of Chenopodium rubrum seedling plants was obtained in continuous light after application of fractions of a partially purified extract from leaves of flowering Maryland Mammoth tobacco (Nicotiana tabacum). The stage of flowal differentiation was dependent on the age of the Chenopodium plants used for the bioassay. Apices of plants treated with the extract at the age of four or seven days showed an advanced branching of the meristem or the beginning of formation of a terminal flower; treatment with the extract of plants 12 d old resulted in rapid formation of flower buds in all assay plants. Non-treated control plants kept in continuous light remained fully vegetative. The effects of the extract on flowering were associated with pronounced growth effects. Floral differentiation was preceeded by elongation of the shoot apex. Extension of all axial organs occurred, while growth of leaves, including leaf primordia, was inhibited. The pattern of growth after application of the flower-inducing substance(s) did not resemble the effects of the known phytohormones, but showed some similarities to growth changes resulting from photoperiodic induction of flowering.

Floral and growth responses in Chenopodium rubrum L. to an extract from flowering Nicotiana tabacum L.

Les effets d'extraits de tabac en floraison sur la structure des apex des types de Chenopodium rubrum sont composes avec ceux obtenus grâce a un traitement avec des phytohormones exogenes. Les modifications de croissance obtenues sont observees sur des coupes transversales des apex, apres coloration, en microscopie optique

The Growth of the Shoot Apex of Chenopodium rubrum L. Treated with a Florigenic Extract from Flowering Tobacco Plants: Preliminary Anatomical Observations

V. N. Lozhnikova

Papers

Photoperiodic control of growth, development and phytohormone balance in Solanum tuberosum

Interaction between day length and phytohormones in the control of potato tuberization in the in vitro culture

Transgenic tobacco plants with T-DNA phytohormone synthesis genes

Floral and growth responses in Chenopodium rubrum L. to an extract from flowering Nicotiana tabacum L.

The Growth of the Shoot Apex of Chenopodium rubrum L. Treated with a Florigenic Extract from Flowering Tobacco Plants: Preliminary Anatomical Observations