Flower initiation marks the transition from vegetative to reproductive growth in seed plants. It is thus a crucial event in the life of these plants, particularly so because of the peculiar relation of vegetative and reproductive development in seed plants which is in turn an outcome of the morphological nature of the flower. Flowers are modified shoots which are produced by modified shoot meristems, the flower primordia. However, once a meristem has been determined as a flower primordium, it is usually unable — except perhaps at the very earliest stages — of reverting to vegetative growth. Vegetative growth and reproductive development in seed plants are thus in a certain sense mutually exclusive; as far as a particular meristem is concerned, flower initiation means the end of its life. The central problem of the physiology of flower initiation is to understand which factors cause a shoot meristem to become a flower primordium, and how they consummate their action.

Physiology of flower initiation

Clonal populations regenerated from single-leaf cell protoplasts of the potato cultivar `Russet Burbank9 display a high frequency of variation for several horticultural and disease resistance characters. Observations over a period of three tuber generations suggest stable changes in tuber shape, yield, and maturity date, in photo-period requirements for flowering, and in plant morphology. Enhanced resistance to early blight (Alternaria solani) and late blight (Phytophthora infestans) diseases also regularly occurs within regenerated populations. These findings are discussed in the context of possible application to varietal improvement, particularly as they pertain to asexually propagated plants.

https://science.sciencemag.org/content/sci/208/4439/17.full.pdf

Potato protoplasts in crop improvement.

Solanum bulbocastanum, a wild, diploid (2n=2x=24) Mexican species, is highly resistant to Phytophthora infestans, the fungus that causes late blight of potato. However this 1 EBN species is virtually impossible to cross directly with potato. PEG-mediated fusion of leaf cells of S. bulbocastanum PI 245310 and the tetraploid potato line S. tuberosum PI 203900 (2n=4x=48) yielded hexaploid (2n= 6x=72) somatic hybrids that retained the high resistance of the S. bulbocastanum parent. RFLP and RAPD analyses confirmed the hybridity of the materials. Four of the somatic hybrids were crossed with potato cultivars Katahdin or Atlantic. The BC1 progeny segregated for resistance to the US8 genotype (A-2 mating type) of P. Infestans. Resistant BC1 lines crossed with susceptible cultivars again yielded populations that segregated for resistance to the fungus. In a 1996 field-plot in Wisconsin, to which no fungicide was applied, two of the BC1 lines, from two different somatic hybrids, yielded 1.36 and 1.32 kg/plant under a severe late-blight epidemic. In contrast, under these same conditions the cultivar Russet Burbank yielded only 0.86 kg/plant. These results indicate that effective resistance to the late-blight fungus in a sexually incompatible Solanum species can be transferred into potato breeding lines by somatic hybridization and that this resistance can then be further transmitted into potato breeding lines by sexual crossing.

Somatic hybrids between Solanum bulbocastanum and potato : a new source of resistance to late blight

Diploid and Polyploid Gametes in Crop Plants: Mechanisms of Formation and Utilization in Plant Breeding

Mature leaves of many plants re-orientate their laminae photonastically in response to non-directional light signals, and/or phototropically in response to directional light signals, by flexing of pulvini, most commonly subtending their bases. (...)

Light-driven leaf movements*

Tuber discs of potato (Solanum tuberosum) growing on a modified Murashige and Skoog medium produced callus and embryoid bodies but failed to form shoots. However, if 0.4 ppm of 6-benzylaminopurine was added to the basal medium, shoots became visible seven weeks after inoculation.

Shoot formation in potato tuber discs in tissue culture

Experiments with green seedlings of sunflower (Helianthus annuns L.) indicate the existence of a phototropic mechanism which involves the leaves or cotyledons, and which can produce an asymmetry of auxin content without the involvement of lateral auxin transport, the classic explanation of phototropism in etiolated seedlings. The basic lines of evidence for the leaf-mediated tropism are: 1) darkening of one cotyledon will cause curvature of the stem toward the lighted cotyledon: 2) the darkened cotyledon sustains an enhanced growth rate in the stem below it: 3) conversely, light suppresses the growth-stimulating effects of a single cotyledon: and 4) more diffusible auxin is obtained from the stem below darkened cotyledons than below lighted ones.

Role of leaves in phototropism.

Regeneration of plantlets from isolated single cells of potato tubers can be achieved through several culturing procedures, each maintained on defined medium and under specific environmental conditions. High auxin and high temperature were favorable for cell proliferation while high cytokinin and alternating low temperature promoted embryoid formation and plantlet regeneration.

Shue-Lock Lam

Papers

Shoot formation in potato tuber discs in tissue culture

Role of leaves in phototropism.

Regeneration of plantlets from single cells in potatoes

Location of a mutant gene causing albinism in a diploid potato

Interaction of temperature and gibberellin on potato seed germination