PECT1, a rate-limiting enzyme in phosphatidylethanolamine biosynthesis, is involved in the regulation of stomatal movement in Arabidopsis.

An Arabidopsis mutant displaying impaired stomatal responses to CO2 , cdi4, was isolated by a leaf thermal imaging screening. The mutated gene PECT1 encodes CTP:phosphorylethanolamine cytidylyltransferase. The cdi4 exhibited a decrease in phosphatidylethanolamine levels and a defect in light-induced stomatal opening as well as low-CO2 -induced stomatal opening. We created RNAi lines in which PECT1 was specifically repressed in guard cells. These lines are impaired in their stomatal responses to low-CO2 concentrations or light. Fungal toxin fusicoccin (FC) promotes stomatal opening by activating plasma membrane H+ -ATPases in guard cells via phosphorylation. Arabidopsis H+ -ATPase1 (AHA1) has been reported to be highly expressed in guard cells, and its activation by FC induces stomatal opening. The cdi4 and PECT1 RNAi lines displayed a reduced stomatal opening response to FC. However, similar to in the wild-type, cdi4 maintained normal levels of phosphorylation and activation of the stomatal H+ -ATPases after FC treatment. Furthermore, the cdi4 displayed normal localization of GFP-AHA1 fusion protein and normal levels of AHA1 transcripts. Based on these results, we discuss how PECT1 could regulate CO2 - and light-induced stomatal movements in guard cells in a manner that is independent and downstream of the activation of H+ -ATPases. [Correction added on 15 May 2023, after first online publication: The third sentence is revised in this version.].

Squatting Throwing Is Not Associated With Increased Medial Elbow Torque in Youth Baseball Catchers.

PURPOSE: To compare medial elbow stress during squatting throwing, standing throwing, and maximum effort throwing and to analyze its relationships with throwing variables and the hip joint internal rotation (IR) range of motion (ROM) in youth baseball catchers. METHODS: Forty-five youth baseball catchers were recruited. Exclusion criteria included pain during throwing, history of surgery, or upper-extremity injuries within 12 months. Catchers performed 5 throws for each of the following throwing conditions: squatting throwing, standing throwing, and maximum effort throwing. Catchers were outfitted with a wearable sensor sleeve that recorded the medial elbow torque, arm speed, and shoulder rotation. Ball velocity was measured using a radar gun. RESULTS: Final analysis included 42 catchers (mean age, 11.5 ± 1.2 years; mean catcher experience, 16.7 ± 10.3 months). The medial elbow torque was significantly greater during maximum effort throwing (19.0 ± 5.2 Nm) than during squatting throwing (14.3 ± 5.4 Nm) and standing throwing (15.7 ± 4.7 Nm) (both P < .001); there was no significant difference between squatting throwing and standing throwing. Multiple linear regression analysis showed that the ball velocity was significantly positively associated with the medial elbow torque during squatting throwing and standing throwing (P = .023 and P = .029, respectively). During squatting throwing, the hip IR ROM on the throwing side was significantly negatively associated with the medial elbow torque (P = .011). CONCLUSIONS: The medial elbow torque during squatting throwing was equivalent to that during standing throwing. Increased medial elbow torque was associated with greater ball velocity during squatting throwing and standing throwing and with decreasing hip joint IR ROM on the throwing side during squatting throwing. Evaluation and stretching of the hip joint IR ROM on the throwing side may be important to decrease elbow stress during squatting throwing in youth baseball catchers. LEVEL OF EVIDENCE: Level II, prospective comparative observational trial.