Abstract
The endosperm of coffee beans is an important structure which is composed of different reserve compounds. In the present work, we followed anatomical features during the reserve mobilization of Coffea arabica L. ‘Catuai’ seed samples, harvested at 20 different sites, after 0, 3, 6, 12, 24, 33 and 45 days of imbibition. Seed samples were properly fixed and stored, respectively, for histochemical and enzyme activity approach. Fixed samples were cross-sectioned for detection of starch, lipids, essential oils, oleoresins, proteins, phenolic compounds, neutral polysaccharides, alkaloids, β-1,3 and β-1,4 glucans, and lignin. Overall, based on histochemical tests and enzyme activity, seed reserve mobilization was similar among the evaluated altitudes and mountainsides. During soaking, there is an intense consumption of reserve compounds, starting at the region close to the embryo. Reserve mobilization intensifies after root protrusion, from 12 days of soaking. The intensification of the reserve consumption is concomitant with an increased activity of MDH is observed at the first 12 days, whereas SOD showed higher expression after 33 days of soaking. At the 33rd day, little reserve is observed in the endosperm. At 45th day, cotyledon leaves are expanded, and the root system, constituted by the taproot and lateral roots, is well established. Key words: Coffea arabica; germination; reserve breakdown; histochemistry; seed anatomy.
Highlights
Coffea arabica L. belongs to family Rubiaceae with its center of origin in Ethiopia
These periods corresponded to events defined as prior to seed soaking (0 days), a short while after soaking (3 days), at half of the time for root protrusion (6 days), at the time expected for root protrusion (12 days), at double the time of root protrusion (24 days), at the recommended time to evaluate germination assays with coffee seeds (30 days), and when cotyledons were already open (45 days)
The availability of seed reserves may contribute to the irregular viability and slow, uneven germination of coffee seeds reported by Reis et al (2010)
Summary
Coffea arabica L. belongs to family Rubiaceae with its center of origin in Ethiopia. Coffee seeds are flat-convex, elliptic or oval, and longitudinally grooved on the flat side and are composed by the embryo; the endosperm; and an envelope called “silver skin”, which is originated from the integument. During the coffee seed germination process, protein hydration, respiration, cell elongation, and structural and enzymatic changes are reported before root protrusion (Selmar et al, 2006), as well as endosperm weakening which accompany further embryo development (Walters; Arendt; Moroni, 2017). The enzyme malate dehydrogenase catalyzes the last reaction of the Krebs cycle (Tunes et al, 2011), being able to transfer electrons from their substrates to generate reduced NAD (P) H or FADH2, which produce ATP via mitochondrial electron transport chain (He et al, 2019) This highlights a vital role in a variety of physiological activities, such as energy metabolism of mitochondria and ERO metabolism in plants (Heber, 1974; Jia et al, 2018), for the germinative process. The aim of the present work study was to observe and describe the morphological and histochemical changes during germination process of coffee seeds harvested in different environments conditions as support for the ongoing research on the improvements of the coffee production system and beverage quality at the Matas de Minas region, Minas Gerais State, Brazil
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