Cytological study of pollen tube growth and early seed development inPetunia inflata

Pollen tube growth from the stigma into the ovule, and the early fruit and seed development following fertilization were examined using fluorescence microscopy, scanning electron microscopy and light microscopy inPetunia inflata. After growing intercellularly in the transmitting tract for 24–36 hr, the pollen tubes emerged into the top part of the ovary cavity and grew along the surface of the septum to reach the ovule. It grew around the furnicle and penetrated the micropyle to enter the embryo sac for fertilization. After fertilization, the endosperm nucleus divided first before the embryo, and the cell wall formation occurred following the division, exhibiting the pattern of cellular type of endosperm development. The first division of the zygote did not occur until 3 days after pollination. At 6 days after pollination, the seeds grew considerably and the endosperm has gone through multiple rounds of cell division. High starch formation in the integument, especially around the embryo sac, was also observed.     

The Solanum lycopersicum AUXIN RESPONSE FACTOR 7 (SlARF7) mediates cross-talk between auxin and gibberellin signalling during tomato fruit set and development

Transgenic tomato plants (Solanum lycopersicum L.) with reduced mRNA levels of AUXIN RESPONSE FACTOR 7 (SlARF7) form parthenocarpic fruits with morphological characteristics that seem to be the result of both increased auxin and gibberellin (GA) responses during fruit growth. This paper presents a more detailed analysis of these transgenic lines. Gene expression analysis of auxin-responsive genes show that SlARF7 may regulate only part of the auxin signalling pathway involved in tomato fruit set and development. Also, part of the GA signalling pathway was affected by the reduced levels of SlARF7 mRNA, as morphological and molecular analyses display similarities between GA-induced fruits and fruits formed by the RNAi SlARF7 lines. Nevertheless, the levels of GAs were strongly reduced compared with that in seeded fruits. These findings indicate that SlARF7 acts as a modifier of both auxin and gibberellin responses during tomato fruit set and development.     

The BRI1-associated kinase 1, BAK1, has a brassinolide-independent role in plant cell-death control

Programmed cell death (PCD) is a common host response to microbial infection [1-3]. In plants, PCD is associated with immunity to biotrophic pathogens, but it can also promote disease upon infection by necrotrophic pathogens [4]. Therefore, plant cell-suicide programs must be strictly controlled. Here we demonstrate that the Arabidopsis thaliana Brassinosteroid Insensitive 1 (BRI1)-associated receptor Kinase 1 (BAK1), which operates as a coreceptor of BRI1 in brassinolide (BL)-dependent plant development, also regulates the containment of microbial infection-induced cell death. BAK1-deficient plants develop spreading necrosis upon infection. This is accompanied by production of reactive oxygen intermediates and results in enhanced susceptibility to necrotrophic fungal pathogens. The exogenous application of BL rescues growth defects of bak1 mutants but fails to restore immunity to fungal infection. Moreover, BL-insensitive and -deficient mutants do not exhibit spreading necrosis or enhanced susceptibility to fungal infections. Together, these findings suggest that plant steroid-hormone signaling is dispensable for the containment of infection-induced PCD. We propose a novel, BL-independent function of BAK1 in plant cell-death control that is distinct from its BL-dependent role in plant development.