The plastochron index: Still useful after nearly six decades

Abstract

The plastochron index (PI) introduced by Erickson and Michelini in 1957 provides a solution to a long-standing problem, of how to measure time in growing plant populations, such that the occurrence of critical developmental events can be more readily detected, compared, and analyzed, than if chronologic time is used. The PI reduces the rather large variation associated with chronologic time in measuring such events by taking advantage of the growth characteristics of stem organs that repeat at regular intervals (the plastochron) and has found widespread application in botanical research. The original formulation and derivation of the PI and associated leaf plastochron index (LPI) is reviewed. Additional formulations that have been developed to overcome some of the limitations of the original PI formulation are examined. Major advancements that have been achieved in understanding the physiology, growth, and development of agriculturally important and current model plant species are reviewed to illustrate how various researchers have used the PI in such studies. Potential uses to which the PI and LPI might be applied in emerging frontiers of plant science are suggested. A searchable bibliography of most all the primary research studies that cite the original PI article is provided.

Phytohormone inhibitor treatments phenocopy brassinosteroid–gibberellin dwarf mutant interactions in maize

“…This difference in node number itself was significantly different than na2‐1 mock‐treated controls for only the PAC treatment, but the delay in flower emergence without additional node production suggests the plastochron depends on BR and GA in maize. The plastochron is the time it takes to initiate each lateral organ from the meristem (Erickson & Michelini, ; Meicenheimer, ). We quantified total number of nodes and time to tassel emergence, so we may overestimate the effect of these treatments on flowering time as decreased elongation should delay emergence of the tassel.…”

Temporal Distinction between Male and Female Floral Organ Development in Nicotiana tabacum cv. Xanthi (Solanaceae)

“…Based on the assumption that plant organs (1) have an exponential phase of growth, (2) grow at equal rates at successive nodes, and (3) initiate equally spaced in time (i.e., constant plastochron) [33], the PI provides a morphological time scale which is reliable for staging development and providing chronological ages of plant organs. Since its establishment, PI has been applied in various species in developmental studies to determine the ages of various plant, mainly floral, organs [36]. This method is further expanded to estimate the PI by an alternative approach when the rate of organ initiation does not remain constant [3,6].…”

Convergence in relationships between leaf traits, spectra and age across diverse canopy environments and two contrasting tropical forests

“…Previous studies linking leaf morphological development (e.g. leaf length) to leaf aging (Erickson & Miche lini, ; Chen et al ., ; Meicenheimer, ) involved laborious measurements over long time periods or relied on uncertain assumptions. Near‐surface remote sensing (e.g.…”