Pollen Tube In Hazel Grows Intermittently:role Of Ca²⁺ And Expression Of Auto-inhibited Ca ²⁺ Pump

Corylus,belonging to Corylus of Betulaceae,is one of the most popular dried fruits in the world.It plays a very important role in domestic economic development and agricultural production.In this experiment,hazelnut pollen was used as experimental material to study the effect of Ca²⁺and the physiological response mechanism of self inhibiting Ca²⁺pump expression in the intermittent growth of hazelnut pollen tube.1.Owing to the absence of the ovary when the female inflorescence blooms,hazel pollen tubes show an obvious intermittent growth pattern,which has an important impact on the number of fruits per cluster and yield,but little is known about the mechanisms governing this process.Spray treatments of Ca²⁺and Ca²⁺-ATPase activator 5-aminolevulinic acid（ALA）in field experiment showed that Ca²⁺treatments inhibited pistillate inflorescence drop and produced more fruits,while the effects of ALA treatments were just opposite to that of calcium treatments.Highly accumulated Ca²⁺was observed at the rear part of the stigma and in the ovary primordial cell layers.2.Under in vitro culture conditions,pollen germination ratio and tube length were promoted and inhibited by Ca²⁺and ALA,respectively.ALA treatment reduced the Ca²⁺concentration in pollen tube,which was not conducive to the formation of a tip-focused Ca²⁺gradient in pollen tube.3.The hazel genome encoded 17 Ca²⁺-ATPases,including 14 auto-inhibited Ca²⁺-ATPases and three ER-type Ca²⁺-ATPases.Hazel Ca²⁺-ATPase family proteins,including 11 com Mon transmembrane domains,were highly conserved.Of 17 Ca²⁺-ATPases,q RT-PCR analysis showed that ChACA1 and ChECA2 were highly expressed in pollen tubes.In the range of 0–1.3m M Ca²⁺,Ca²⁺fluorescence intensity in pollen tubes,expression of ChACA1 continued to rise simultaneously,and they reached their maximum at 1.3 m M Ca²⁺,then declined at 1.6 m M Ca²⁺,which was consistent and inconsistent with changing trends of pollen tube length and ChECA2respectively.Analysis of enzyme activity in pollen tubes showed that Ca²⁺-ATPase activity was promoted by both Ca²⁺and ALA treatments significantly.4.Our findings suggested that ChACA1 may act as a key regulator of pollen germination and pollen tube development in hazel,and provide new insight into the mechanisms of unique pollen tube intermittent growth in hazel.