title: Differences in proleptic and epicormic shoot structures in relation to water deficit and growth rate in almond trees (Prunus dulcis).
abstract: OBJECTIVE
  Shoot characteristics differ depending on the meristem tissue that they originate from and environmental conditions during their development. This study focused on the effects of plant water status on axillary meristem fate and flowering patterns along proleptic and epicormic shoots, as well as on shoot growth rates on 'Nonpareil' almond trees (Prunus dulcis). The aims were (1) to characterize the structural differences between proleptic and epicormic shoots, (2) to determine whether water deficits modify shoot structures differently depending on shoot type, and (3) to determine whether shoot structures are related to shoot growth rates.
  
  
  METHODS
  A hidden semi-Markov model of the axillary meristem fate and number of flower buds per node was built for two shoot types growing on trees exposed to three plant water status treatments. The models segmented observed shoots into successive homogeneous zones, which were compared between treatments. Shoot growth rates were calculated from shoot extension measurements made during the growing season.
  
  
  RESULTS
  Proleptic shoots had seven successive homogeneous zones while epicormic shoots had five zones. Shoot structures were associated with changes in growth rate over the season. Water deficit (1) affected the occurrence and lengths of the first zones of proleptic shoots, but only the occurrence of the third zone was reduced in epicormic shoots; (2) had a minor effect on zone flowering patterns and did not modify shoot or zone composition of axillary meristem fates; and (3) reduced growth rates, although patterns over the season were similar among treatments.
  
  
  CONCLUSIONS
  Two meristem types, with different latency durations, produced shoots with different growth rates and distinct structures. Differences between shoot type structure responses to water deficit appeared to reflect their ontogenetic characteristics and/or resource availability for their development. Tree water deficit appeared to stimulate a more rapid progression through ontogenetic states.
authors.affiliation: Department of Plant Sciences, University of California, Davis, CA 95616, USA.
authors.forename: Claudia
authors.initials: C
authors.lastname: Negrón
authors.forename: Loreto
authors.initials: L
authors.lastname: Contador
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Lampinen
authors.forename: Samuel G
authors.initials: SG
authors.lastname: Metcalf
authors.forename: Yann
authors.initials: Y
authors.lastname: Guédon
authors.forename: Evelyne
authors.initials: E
authors.lastname: Costes
authors.forename: Theodore M
authors.initials: TM
authors.lastname: DeJong
mesh_terms: D003681:Dehydration; D035264:Flowers / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology; D008390:Markov Chains; D018519:Meristem / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology; D018520:Plant Shoots / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology; D027861:Prunus / Q000033:anatomy & histology* / Q000254:growth & development* / Q000502:physiology; D012621:Seasons; D013312:Stress, Physiological; D013997:Time Factors; D014197:Trees
keywords: Almond tree; Prunus dulcis; branching pattern; epicormic shoots; flowering; hidden semi-Markov model; proleptic shoots; shoot growth; water deficit