Recent developments in mesophyll conductance in C3, C4, and crassulacean acid metabolism plants

The conductance of carbon dioxide (CO₂) from the substomatal cavities to the initial sites of CO₂ fixation (g_m) can significantly reduce the availability of CO₂ for photosynthesis. There have been many recent reviews on: (i) the importance of g_m for accurately modelling net rates of CO₂ assimilation, (ii) on how leaf biochemical and anatomical factors influence g_m, (iii) the technical limitation of estimating g_m, which cannot be directly measured, and (iv) how g_m responds to long‐ and short‐term changes in growth and measurement environmental conditions. Therefore, this review will highlight these previous publications but will attempt not to repeat what has already been published. We will instead initially focus on the recent developments on the two‐resistance model of g_m that describe the potential of photorespiratory and respiratory CO₂ released within the mitochondria to diffuse directly into both the chloroplast and the cytosol. Subsequently, we summarize recent developments in the three‐dimensional (3‐D) reaction‐diffusion models and 3‐D image analysis that are providing new insights into how the complex structure and organization of the leaf influences g_m. Finally, because most of the reviews and literature on g_m have traditionally focused on C₃ plants we review in the final sections some of the recent developments, current understanding and measurement techniques of g_m in C₄ and crassulacean acid metabolism (CAM) plants. These plants have both specialized leaf anatomy and either a spatially or temporally separated CO₂ concentrating mechanisms (C₄ and CAM, respectively) that influence how we interpret and estimate g_m compared with a C₃ plants.     

Mechanobiology of conjunctival epithelial cells exposed to wall shear stresses

Biomechanics and Modeling in Mechanobiology - The human conjunctival epithelial cells (HCEC) line the inner sides of the eyelids and the anterior part of the sclera. They include goblet cells that...     

AUXIN RESPONSE FACTOR 2 Intersects Hormonal Signals in the Regulation of Tomato Fruit Ripening

The involvement of ethylene in fruit ripening is well documented, though knowledge regarding the crosstalk between ethylene and other hormones in ripening is lacking. We discovered that AUXIN RESPONSE FACTOR 2A (ARF2A), a recognized auxin signaling component, functions in the control of ripening. ARF2A expression is ripening regulated and reduced in the rin, nor and nr ripening mutants. It is also responsive to exogenous application of ethylene, auxin and abscisic acid (ABA). Over-expressing ARF2A in tomato resulted in blotchy ripening in which certain fruit regions turn red and possess accelerated ripening. ARF2A over-expressing fruit displayed early ethylene emission and ethylene signaling inhibition delayed their ripening phenotype, suggesting ethylene dependency. Both green and red fruit regions showed the induction of ethylene signaling components and master regulators of ripening. Comprehensive hormone profiling revealed that altered ARF2A expression in fruit significantly modified abscisates, cytokinins and salicylic acid while gibberellic acid and auxin metabolites were unaffected. Silencing of ARF2A further validated these observations as reducing ARF2A expression let to retarded fruit ripening, parthenocarpy and a disturbed hormonal profile. Finally, we show that ARF2A both homodimerizes and interacts with the ABA STRESS RIPENING (ASR1) protein, suggesting that ASR1 might be linking ABA and ethylene-dependent ripening. These results revealed that ARF2A interconnects signals of ethylene and additional hormones to co-ordinate the capacity of fruit tissue to initiate the complex ripening process.     

Arabidopsis HSP70‐16 is required for flower opening under normal or mild heat stress temperatures

Sepals play important roles in protecting inner floral organs from various stresses and in guaranteeing timely flower opening. However, the exact role of sepals in coordinating interior and exterior signals remains elusive. In this study, we functionally characterized a heat shock protein gene, Arabidopsis HSP70‐16, in flower opening and mild heat stress response, using combined genetics with anatomic, physiological, chemical, and molecular analyses. We showed that HSP70‐16 is required for flower opening and mild heat response. Mutation of HSP70‐16 led to a significant reduction in seed setting rate under 22°C, which was more severe at 27°C. Mutation of HSP70‐16 also caused postgenital fusion at overlapping tips of two lateral sepals, leading to failed flower opening, abnormal floral organ formation, and impaired fertilization and seed setting. Chemical and anatomic analyses confirmed specific chemical and morphological changes of cuticle property in mutant lateral sepals, and qRT‐PCR data indicated that expression levels of different sets of cuticle regulatory and biosynthetic genes were altered in mutants grown at both 22°C and 27°C temperatures. This study provides a link between thermal and developmental perception signals and expands the understanding of the roles of sepal in plant development and heat response.     

Transgenic maize phosphoenolpyruvate carboxylase alters leaf–atmosphere CO2 and 13CO2 exchanges in Oryza sativa

Photosynthesis Research - The engineering process of C4 photosynthesis into C3 plants requires an increased activity of phosphoenolpyruvate carboxylase (PEPC) in the cytosol of leaf mesophyll...     

Terpenoid metabolism in wild-type and transgenic Arabidopsis plants

Volatile components, such as terpenoids, are emitted from aerial parts of plants and play a major role in the interaction between plants and their environment. Analysis of the composition and emission pattern of volatiles in the model plant Arabidopsis showed that a range of volatile components are released, primarily from flowers. Most of the volatiles detected were monoterpenes and sesquiterpenes, which in contrast to other volatiles showed a diurnal emission pattern. The active terpenoid metabolism in wild-type Arabidopsis provoked us to conduct an additional set of experiments in which transgenic Arabidopsis overexpressing two different terpene synthases were generated. Leaves of transgenic plants constitutively expressing a dual linalool/nerolidol synthase in the plastids (FaNES1) produced linalool and its glycosylated and hydroxylated derivatives. The sum of glycosylated components was in some of the transgenic lines up to 40- to 60-fold higher than the sum of the corresponding free alcohols. Surprisingly, we also detected the production and emission of nerolidol, albeit at a low level, suggesting that a small pool of its precursor farnesyl diphosphate is present in the plastids. Transgenic lines with strong transgene expression showed growth retardation, possibly as a result of the depletion of isoprenoid precursors in the plastids. In dual-choice assays with Myzus persicae, the FaNES1-expressing lines significantly repelled the aphids. Overexpression of a typical cytosolic sesquiterpene synthase resulted in the production of only trace amounts of the expected sesquiterpene, suggesting tight control of the cytosolic pool of farnesyl diphosphate, the precursor for sesquiterpenoid biosynthesis. This study further demonstrates the value of Arabidopsis for studies of the biosynthesis and ecological role of terpenoids and provides new insights into their metabolism in wild-type and transgenic plants.