Short alternating light/dark periods priming improves tobacco (Nicotiana tabacum L.) tolerance to clomazone herbicide: growth, chlorophyll a fluorescence transient and photosynthesis rate

Nicotiana tabacum L. cv. Virginie vk51 seedlings at the three-leaf stage were grown in a hydroponic culture system. Those seedlings were subjected to a photoperiod priming treatment with alternating light/dark periods (AL) (16 min light/8 min dark cycles and a photosynthetic photon flux density (PPFD) of 50 μmol photons m⁻² s⁻¹) for 3 days. After 2 weeks, the plantlets were transferred to two soil types with 0 (control) or 100 µM clomazone. Compared with the non-primed plants, the AL-primed plants exhibited greater clomazone tolerance with respect to all of the growth parameters and during all of the growth stages. This AL priming effect was demonstrated by increases in plant leaf area and dry and fresh plant weights, which might have been related to increases in the CO₂ assimilation rate (P_n and P_max). Furthermore, the reduced photon absorption (ABS/RC) and heat dissipation (DI0/RC) rates as well as the observed increase in photosystem II (PSII) efficiency (the maximum quantum yield of PSII (F_v/F_m), photochemical quenching (qP), actual PSII efficiency (Ф_PSII)) and electron transport (the light-saturated electron transport rate (ETR) and electron flux beyond the first quinone electron acceptor of PSII (Q_A) evaluated as (1–V_J)) provide strong evidence of a higher tolerance to clomazone. Collectively, these results suggest that AL priming treatment could potentially improve the protection or production of other transplanted species.