X-ray phase contrast imaging of Vitis spp. buds shows freezing pattern and correlation between volume and cold hardiness

Abstract

Grapevine (Vitis spp.) buds must survive winter temperatures in order to resume growth when suitable conditions return in spring. They do so by developing cold hardiness through deep supercooling, but the mechanistic process of supercooling in buds remains largely unknown. Here we use synchrotron X-ray phase contrast imaging to study cold hardiness-related characteristics of V. amurensis, V. riparia, and V. vinifera buds: time-resolved 2D imaging was used to visualize freezing; and microtomography was used to evaluate morphological changes during deacclimation. Bud cold hardiness was determined (low temperature exotherms; LTEs) using needle thermocouples during 2D imaging as buds were cooled with a N2 gas cryostream. Resolution in 2D imaging did not allow for ice crystal identification, but freezing was assessed by movement of tissues coinciding with LTE values. Freezing was observed to propagate from the center of the bud toward the outer bud scales. The freezing events observed lasted several minutes. Additionally, loss of supercooling ability appears to be correlated with increases in bud tissue volume during the process of deacclimation, but major increases in volume occur after most of the supercooling ability is lost, suggesting growth resumption processes are limited by deacclimation state.

Vein‐to‐blade ratio is an allometric indicator of leaf size and plasticity

“…Because we matched nodes by mature leaves counting from the base of the shoot, a large proportion of the leaves analyzed in this study were not neoformed the year of harvest and potentially influenced by the climate of the previous year in which they initiated. Considering that the buds are frozen during the winter (Londo and Kovaleski, 2017, 2019; Kovaleski et al, 2018; Kovaleski and Londo, 2019), we chose two windows over which we averaged daily climate variables: “previous year” is the average inclusive of March to November of the previous year, “current year” inclusive of March to June of the year of harvest.…”

Woody species do not differ in dormancy progression: Differences in time to budbreak due to forcing and cold hardiness

“…This demonstrates the existence of a phenotype that is measured easily (although requiring some instrumentation) and much more so than determination of internal development of buds (e.g., refs. 66 and 67 ) and that can be measured prior to any external development in budbreak progression. In addition, cold hardiness dynamics clearly demonstrate the negative relationship between chilling and forcing (as plasticity) ( 15 , 17 , 33 ), indicating that this is not a measurement artifact ( 2 ).…”

Time to budbreak is not enough: cold hardiness evaluation is necessary in dormancy and spring phenology studies

“…Examples here are based on extensive phenotyping of plants that use supercooling as a mechanism of cold hardiness, but we expect a similar dynamic for plants that use other mechanisms (Neuner et al, 2019; Villouta et al, 2020). Under forcing (i.e., exposure to warm temperatures and generally long days), supercooling ability is lost linearly, without changes in external morphology (Box 1a ) [but internal anatomical and morphological changes occur (Viherä-Aarnio et al, 2014; Xie et al, 2018; Kovaleski et al, 2019; Villouta et al, 2022)]. As growth resumes, the supercooling ability has been lost and concentration mostly drives cold hardiness of tissues.…”