On the Cover: Guard cells use an elegant signaling pathway to regulate the aperture of stomata, pores that facilitate gas exchange. In response to abscisic acid (ABA), reactive oxygen species (ROS) are produced in a transient burst acting as second messengers to induce stomatal closure. ROS concentrations must be tightly regulated by an antioxidant network that minimizes ROS concentrations, preventing oxidative damage and modulating ROS signaling within the cell. In this issue, Watkins et al. (pp. 1707–1717) test the hypothesis that accumulation of flavonols acts to modulate ROS in guard cells, but not surrounding pavement cells. Flavonol accumulation and ROS levels were visualized by fluorescent dyes, illustrating that flavonols accumulate in guard cells, reducing ROS levels in the wild type. In guard cells of tt4, a flavonoid-deficient mutant, ROS levels are elevated over the wild type. The increased ROS in tt4 was sufficient to enhance ABA-dependent stomatal closure. Watkins et al. also observed increased flavonol accumulation in response to ethylene, resulting in a further reduction of ROS concentrations and inhibited stomatal closure in response to ABA. The cover shows an epifluorescent image of a whole leaf stained with a flavonol-specific fluorescent dye (yellow) and chlorophyll autofluorescence (red) imaged at 100× magnification. Cover image credits: Justin Watkins and Gloria Muday.
PLANT PHYSIOLOGY: 德国科学家解析一个内质网ATP转运子的功能
定位于内质网的ATP/ADP-antiporter (ER-ANT1)是维管植物所特有的一类基因，这类基因参与了对内质网的能量供应过程，目前关于ER-ANT1的功能尚不清楚。
本研究显示，er-ant1突变体的光呼吸伴随甘氨酸水平增高以及生长受抑制的表型，酶学分析显示甘氨酸脱羧酶的活性受到抑制。
作者发现，另外一个功能尚未明确的HaloAcid Dehalogenase (HAD)-like hydrolase family基因的突变可以恢复上述er-ant1突变体的表型。
基因定位分析显示，该HAD基因定位于叶绿体中，特异性的脱磷酸化B6 vitamer pyridoxal 50-phosphate(PLP)。生理实验显示，在er-ant1突变体中vitamin B6的平衡受损，添加vitamin B6（pyridoxine,PN)可以部分恢复er-ant1突变体表型，这证明了是叶绿体代谢失衡导致了er-ant1的生长发育缺陷。
原文信息 Loss of a pyridoxal-phosphate phosphatase rescues Arabidopsis lacking an endoplasmic reticulum ATP carrier
