Pericarp, Leachate, and Carbohydrate Involvement in Thermoinhibition of Germinating Spinach Seeds

Abstract

<jats:p>Spinach (<jats:italic>Spinacia oleracea</jats:italic> L.) seed germination can be inhibited by high temperatures. An understanding of thermoinhibition in spinach is critical in predicting germination and emergence events. The purpose of this study was 3-fold: 1) to determine seed germination percentage and rate of spinach genotypes—`Cascade', `ACX 5044', `Fall Green', and `ARK 88-354'—exposed to constant and alternating temperatures; 2) to determine the nature and extent of inhibition imposed by the pericarp; and 3) to investigate leachate and oligosaccharide involvement in thermoinhibition. Germination inhibition began at &gt;20 °C constant temperature and was totally suppressed at 35 °C. Alternating temperatures at 30/15 °C (12-hour day/12-hour night) resulted in greater germination than a constant 30 °C. The genotype sensitivity to supraoptimal temperatures was in the order of `ARK 88-354' ≤ `Fall Green' &lt; `ACX 5044' &lt; `Cascade', but the highly thermoinhibited `Cascade' seeds retained the ability to germinate when shifted to lower incubation temperatures. The pericarp inhibited germination, since seeds deprived of the pericarp had ≈90% germination at 30 °C. `ACX 5044' and `Cascade' had higher ABA content in the pericarp than `ARK 88-354' and `Fall Green'. Before imbibition at 30 °C, raffinose levels in each genotype were in the order of `ARK 88-354' &gt; `Fall Green' &gt; `Cascade'. After 48 hours of imbibition, sucrose and glucose levels were highest and raffinose levels were lowest in `ARK 88-354' and `Fall Green' seeds, while `Cascade' seeds remained less active metabolically. These data suggest that the pericarp apparently acts as a physical barrier as well as a source of inhibitors during thermoinhibition.</jats:p>

Factors contributing to the regulation of thermoinhibition in Tagetes minuta L.

“…Abscisic acid (ABA) is the hormone most commonly associated with the imposition and maintenance of thermoinhibition (Dutta et al, 1994, Yoshioka et al, 1998;Leskovar et al, 1999;Gonia et al, 2004), while the gibberellins, GA 3 (Persson, 1993;Small et al, 1993;Dutta et al, 1994Dutta et al, , 1997Carter and Stevens, 1998) as well as GA 4+7 (Drewes, 1989;Madakadze et al, 1993), and ethylene (Huang and Khan, 1992;Prusinski and Khan, 1993;Gallardo et al, 1994;Carter and Stevens, 1998) are the phytohormones most commonly associated with the alleviation thereof. ABA/ ethylene interaction models have also been proposed in which ABA interferes in the production of ethylene (Gallardo et al, 1994).…”

Effect of Temperature on Seed Germination in Spinach (Spinacia oleracea)

“…Prior experiments have shown that spinach seeds will germinate in soil temperatures from 5 to 30°C with germination percentages highest at 20°C and dropping abruptly between 25 and 30°C (Atherton and Farooque, 1983). Spinach seed germination has been reported to cease entirely at 35°C (Leskovar and Esensee, 1999). Substantial seedling root development requires temperatures above 18.9°C, and top growth will be limited at temperatures below 12.3°C and above 23.3°C (Wilcox and Pfeiffer, 1990).…”

Optimal Irrigation for Onion and Celery Production and Spinach Seed Germination in Histosols

“…For spinach seed germination, high moisture at the surface is essential. Because spinach is shallowly seeded, there may be a rapid fluctuation of soil moisture around the seeds, especially during the warmer months, when an increase in soil temperatures in the seed zone can inhibit seed germination (Leskovar et al, 1999). Germination and emergence of spinach seeds is delayed and reduced as soil water availability decreases, leading to poor stand establishment in the field and consequently to yield losses (Katzman et al, 2001).…”