Manipulation of the hypocotyl sink activity by reciprocal grafting of two <i>Raphanus sativus</i> varieties: its effects on morphological and physiological traits of source leaves and whole‐plant growth

<jats:title>Abstract</jats:title><jats:p>To reveal whether hypocotyl sink activities are regulated by the aboveground parts, and whether physiology and morphology of source leaves are affected by the hypocotyl sink activities, we conducted grafting experiments using two <jats:styled-content style="fixed-case"><jats:italic>R</jats:italic></jats:styled-content><jats:italic>aphanus sativus</jats:italic> varieties with different hypocotyl sink activities. Comet (<jats:styled-content style="fixed-case">C</jats:styled-content>) and Leafy (<jats:styled-content style="fixed-case">L</jats:styled-content>) varieties with high and low hypocotyl sink activities were reciprocally grafted and resultant plants were called by their scion and stock such as <jats:styled-content style="fixed-case">CC</jats:styled-content>, <jats:styled-content style="fixed-case">LC</jats:styled-content>, <jats:styled-content style="fixed-case">CL</jats:styled-content> and <jats:styled-content style="fixed-case">LL</jats:styled-content>. Growth, leaf mass per area (<jats:styled-content style="fixed-case">LMA</jats:styled-content>), total non‐structural carbohydrates (<jats:styled-content style="fixed-case">TNC</jats:styled-content>s) and photosynthetic characteristics were compared among them. Comet hypocotyls in <jats:styled-content style="fixed-case">CC</jats:styled-content> and <jats:styled-content style="fixed-case">LC</jats:styled-content> grew well regardless of the scions, whereas Leafy hypocotyls in <jats:styled-content style="fixed-case">CL</jats:styled-content> and <jats:styled-content style="fixed-case">LL</jats:styled-content> did not. Relative growth rate was highest in <jats:styled-content style="fixed-case">LL</jats:styled-content> and lowest in <jats:styled-content style="fixed-case">CC</jats:styled-content>. Photosynthetic capacity was correlated with <jats:styled-content style="fixed-case">Rubisco</jats:styled-content> (ribulose 1·5‐bisphosphate carboxylase/oxygenase) content but unaffected by <jats:styled-content style="fixed-case">TNC</jats:styled-content>. High <jats:styled-content style="fixed-case">C</jats:styled-content>/<jats:styled-content style="fixed-case">N</jats:styled-content> ratio and accumulation of <jats:styled-content style="fixed-case">TNC</jats:styled-content> led to high <jats:styled-content style="fixed-case">LMA</jats:styled-content> and structural <jats:styled-content style="fixed-case">LMA</jats:styled-content>. These results showed that the hypocotyl sink activity was autonomously regulated by hypocotyl and that the down‐regulation of photosynthesis was not induced by <jats:styled-content style="fixed-case">TNC</jats:styled-content>. We conclude that the change in the sink activity alters whole‐plant growth through the changes in both biomass allocation and leaf morphological characteristics in <jats:styled-content style="fixed-case"><jats:italic>R</jats:italic></jats:styled-content><jats:italic>. sativus</jats:italic>.</jats:p>