Phytohormones play crucial roles in fruit set regulation and development. Here, gibberellins (GA4+7), but not GA3, induced pear parthenocarpy. To systematically investigate the changes upon GA4+7 induced pear parthenocarpy, dynamic changes in histology, hormone and transcript levels were observed and identified in unpollinated, pollinated and GA4+7-treated ovaries. Mesocarp cells continued developing in both GA4+7-treated and pollinated ovaries. In unpollinated ovaries, mesocarp cells stopped developing 14 days after anthesis. During fruit set process, GA4+7, but not GA1+3, increased after pollination. Abscisic acid (ABA) accumulation was significantly repressed by GA4+7 or pollination, but under unpollinated conditions, ABA was produced in large quantities. Moreover, indole-3-acetic acid biosynthesis was not induced by GA4+7 or pollination treatments. Details of this GA–auxin–ABA cross-linked gene network were determined by a comparative transcriptome analysis. The indole-3-acetic acid transport-related genes, mainly auxin efflux carrier component genes, were induced in both GA4+7-treated and pollinated ovaries. ABA biosynthetic genes of the 9-cis-epoxycarotenoid dioxygenase family were repressed by GA4+7 and pollination. Moreover, directly related genes in the downstream parthenocarpy network involved in cell division and expansion (upregulated), and MADS-box family genes (downregulated), were also identified. Thus, a model of GA-induced hormonal balance and its effects on parthenocarpy were established.
Understanding
ripening and senescence processes in postharvest
stored fruit is key to the identification and implementation of effective
treatment methods. Here, we explored the effects of exogenous applications
of melatonin (MT) and nitric oxide (NO) on ripening and softening
processes in three cultivars of European pear (Pyrus
communis L.). The results showed that MT and NO played
important roles in the two processes: they decreased the rate of upregulation
of PcCel and PcPG, inhibited expression
of ethylene synthetase genes (PcACS and PcACO), and reduced rates of respiration and ethylene production. MT increased
activity of NO synthase through upregulation of expression of PcNOS that subsequently led to an increase in NO content.
However, when NO synthesis was inhibited, the delaying effect of MT
on fruit senescence was almost eliminated. These findings indicate
that MT acted on the upstream process of NO synthesis that then delayed
senescence in pear fruit.
Plasmonic reflectors based on serial stub structure are studied in this paper. A general theory of periodic stub structure using transmission line model is developed. The transmission characteristics, e.g., periodicity and symmetry of the spectra, are closely related to the ratio of structure period to stub length. Investigation reveals that the transmission valleys of the spectra could be divided into two categories, which is quite different from conventional Bragg reflectors. Finite-Difference Time-Domain (FDTD) method is used in numerical analysis in this paper.
Three-dimensional
(3D) light fields with spatially inhomogeneous
polarization and intensity distributions play an increasingly important
role in photonics due to their peculiar optical features and extra
degrees of freedom for carrying information. However, it is very challenging
to simultaneously control the intensity profile and polarization profile
in an arbitrary manner. Here we experimentally demonstrate a metalens
that can focus light into an arbitrarily shaped focal curve with a
predefined polarization distribution. The efficacy of this approach
is exemplified through the demonstration of focused curves in 3D space
ranging from simple shapes such as a circle to topologically nontrivial
objects such as a 3D knot with controlled local polarization states.
This powerful control of the light field would be technically challenging
with their conventional counterparts. Our demonstration may find applications
in beam engineering and integration optics.
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