Small-seeded Hakea species tolerate cotyledon loss better than large-seeded congeners

Sh-Hoob El-Amhir,George Yan,Tianhua He,Byron B Lamont

doi:10.1038/srep41520

Sh-Hoob El-Amhir, George Yan + Show 2 more

Open Access

https://doi.org/10.1038/srep41520

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Abstract

Six Hakea species varying greatly in seed size were selected for cotyledon damage experiments. The growth of seedlings with cotyledons partially or completely removed was monitored over 90 days. All seedlings perished by the fifth week when both cotyledons were removed irrespective of seed size. Partial removal of cotyledons caused a significant delay in the emergence of the first leaf, and reduction in root and shoot growth of the large-seeded species. The growth of seedlings of small-seeded species was less impacted by cotyledon damage. The rate of survival, root and shoot lengths and dry biomass of the seedlings were determined after 90 days. When seedlings were treated with balanced nutrient solutions following removal of the cotyledons, survival was 95–98%, but 0% when supplied with nutrient solutions lacking N or P or with water only. The addition of a balanced nutrient solution failed to restore complete growth of any species, but the rate of root elongation for the small-seeded species was maintained. Cotyledons provide nutrients to support early growth of Hakea seedlings, but other physiological roles for the cotyledons are also implicated. In conclusion, small-seeded Hakea species can tolerate cotyledons loss better than large-seeded species.

Highlights

Restored the growth of the seedlings to those with intact cotyledons
Little is known about the association between seed size and cotyledon damage and the ability of seedlings to respond to various degrees of cotyledon damage
Using Australian Hakea species as a model, the objectives of this study were to: 1) investigate the effects of the partial or complete removal of cotyledons on the early growth of seedlings to determine to what extent Hakea species tolerate cotyledon damage; 2) explore the role of seed size in mitigating the negative impact of the partial or complete removal of the cotyledons on the early growth of seedlings; and 3) investigate whether the loss of cotyledons could be compensated for by the addition of critical nutrients to the soil, and if so whether such ability is seed-size dependent

Summary

Introduction

Restored the growth of the seedlings to those with intact cotyledons. It is not clear whether the seedlings rely only on N and P in the cotyledon reserve or they acquire some N and P from the soil at an early stage of growth. Despite the importance of cotyledons in the regeneration of plants[18,19], some of the factors affecting seedling survival, including the interaction between seed size, seedlings and herbivores, are not completely clear[20] It remains equivocal whether seedlings can survive and establish solely on the nutrients in the soil, N and P, and whether the role of seed size is important in the acquisition of nutrients after the cotyledons are damaged. Using Australian Hakea species as a model, the objectives of this study were to: 1) investigate the effects of the partial or complete removal of cotyledons on the early growth of seedlings to determine to what extent Hakea species tolerate cotyledon damage; 2) explore the role of seed (cotyledon) size in mitigating the negative impact of the partial or complete removal of the cotyledons on the early growth of seedlings; and 3) investigate whether the loss of cotyledons could be compensated for by the addition of critical nutrients to the soil, and if so whether such ability is seed-size dependent

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